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Pfizer -BioNTech COVID -19 Vaccine
C4591022 NON -INTERVENTIONAL STUDY STATISTICAL ANALYSIS PLAN
Version 2.0, 05 May 2022 
PFIZER CONFIDENTIAL 
Page 1NON -INTERVENTIONAL (NI) STUDY STATISTICAL ANALYSIS PLAN (SAP)
Study Information
Title Pfizer -BioNTech COVID -19 Vaccine 
Exposure during Pregnancy : A Non-
Interventional Post -Approval Safet y Study 
of Pregnancy  and Infant Outcomes in the 
Organization of Teratology  Information 
Specialists (OTI S)/MotherToBaby  
Pregnancy  Registry
Protocol number C4591022
Statistical Analysis Plan version identifier 2.0
Date 05 May  2022
EU Post Authorization Study (PAS) 
register numberEUPAS42869
Active substance COVID- 19 mRNA Vaccine is single -
stranded, 5’- capped messenger RNA 
(mRNA) produced using a cell -free in vitro 
transcription from the corresponding DNA 
templates, encoding the viral spike (S) 
protein of SARS -CoV -2
Medicinal product Pfizer -BioNTech COVID -19 Vaccine 
(BNT162b2)
Research question and objectives Research Question: Is the risk of pregnancy 
andinfant safety  outcomes increased among 
pregnant women in the Organization of 
Teratology  Information Specialists 
(OTIS)/MotherToBab y Pregnancy  Registry
who were vaccinated with the Pfizer -
BioNTech COVID -19 vaccine during 
pregnancy  compared with those who did not 
receive an y COVID -19 vaccine during 
pregnancy ?
Study  Objective
To assess whether pregnant women 
who received the Pfizer -BioNTech 
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Page 31.TABLE OF CONTENTS
1. TABLE OF CONTENTS ................................ ................................ ................................ .......3
2. LIST OF ABBREVIAT IONS ................................ ................................ ................................ 5
3. AMENDMENTS AND UP DATES ................................ ................................ ....................... 7
4. RATIONALE AND BACKGROUND (SUMMARY) .........................................................8
5. RESEARCH QUESTION AND OBJECTI VE................................ ................................ ......8
6. STUDY DESIGN (SUM MARY) ................................ ................................ .......................... 9
7. STUDY POPUL ATION (SUM MARY) ................................ ................................ .............. 10
7.1. I nclusion Criteria ................................ ................................ ................................ .....10
7.2. Exclusion Criteria ................................ ................................ ................................ ....10
7.3. Follow -Up................................ ................................ ................................ ............... 10
8. STUDY SIZE ................................ ................................ ................................ ....................... 11
8.1. Sample Size ................................ ................................ ................................ ............. 11
8.2. Power Calculations ................................ ................................ ................................ ..11
9. DATA SOURCE (SUMMARY) ................................ ................................ ......................... 13
9.1. Maternal Interviews ................................ ................................ ................................ .13
9.2. Medical Records and General Pediatric Evaluation................................ ................ 15
10. VARIABLES ................................ ................................ ................................ ..................... 16
10.1. Timing Variables ................................ ................................ ................................ ...16
10.2. Identification of Exposure and Comparator ................................ ......................... 16
10.3. Classification of Pregnancy  and Infant Outcomes ................................ ................ 20
10.3.1. Major Congenital Malformations ................................ ............................. 20
10.3.2. Spontaneous abortion ................................ ................................ ................ 22
10.3.3. Elective termination/abortion ................................ ................................ ...22
10.3.4. Stillbirth ................................ ................................ ................................ ....22
10.3.5. Preterm delivery ................................ ................................ ........................ 22
10.3.6. Small for gestational age at birth ................................ .............................. 22
10.3.7. Small for age postnatal growth at one year of age ................................ ....22
10.4. Demographic and Clinical Characteristics ................................ ............................ 23
11. MI SSING DATA................................ ................................ ................................ ............... 26
12. STATI STICAL METH ODS AND DATA ANALYSI S ................................ ................... 27
12.1. Data Cleaning and Preparation of Datasets ................................ ........................... 27
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Page 412.2. Demographic and Baseline Characteristics................................ ........................... 27
12.3. Primary  Anal yses................................ ................................ ................................ ..27
12.3.1. Major Congenital Malformation ................................ ............................... 30
12.3.2. Spontaneous Abortion, Stillbirth, and Preterm Delivery.......................... 31
12.3.3. Elective Termination/Abortion................................ ................................ .33
12.3.4. Small for Gestational Age at Birth and Small for Age Postnatal 
Growth at One Year of Age ................................ ................................ ............. 33
12.4. Secondary  Anal yses................................ ................................ .............................. 34
12.4.1. Stratified/Subgroup Analy ses................................ ................................ ...34
12.4.2. I ndividual Dose Effects ................................ ................................ ............ 34
12.4.3. Evaluation for a Pattern of Major Congenital Malformatio ns.................. 38
12.4.4. L ost to Follow -Up................................ ................................ ..................... 38
12.5. Sensitivity  Anal yses................................ ................................ .............................. 39
12.6. I nterim Anal yses................................ ................................ ................................ ...39
12.7. Analy sis Software ................................ ................................ ................................ .40
13. REFERENCES ................................ ................................ ................................ .................. 40
14. LIST OF TABLES ................................ ................................ ................................ ............. 44
15. LIST OF FIGURES ................................ ................................ ................................ ........... 44
ANNEX 1. LIST OF STAND- ALONE DOCUMENTS ................................ ......................... 44
ANNEX 2. ADDITIONAL  INFORMATION ................................ ................................ ......... 44
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Page 52. LIST OF ABBREVIATIONS
Abbreviation Definition
BMI body  mass index 
CDCCenters for Disease Control and Prevention  
CI confidence interval
cm centimeter
COVID -19 Coronavirus disease 2019
EUA Emergency  Use Authorization
FDA Food and Drug Administration
HCP health care provider
HR hazard ratio
IPTW inverse probability of treatment weighting
kg kilogram
LMP last menstrual period
m meter
MACDP Metropolitan Atlanta Congenital Defects Program
MI multiple imputation
MICE multivariate imputation by  chained equations
mRNA messenger ribonucleic acid
MSM marginal structural model
NCHS National Center for Health Statistics
OR odds ratio
OTIS Organization of Teratology  Information Specialists
PASS Post-Authorization Safety  Study
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Page 6Abbreviation Definition
PCR polymerase chain reaction
PDA patent ductus arteriosus 
PFO patent foramen ovale 
PMC postmarketing commitment
RNA ribonucleic acid
RR risk ratio
SAP Statistical Analy sis Plan
SARS -CoV -2 severe acute respiratory  syndrome coronavirus 2 
SMD standardized mean difference
SOP standard operating procedure
Tdap tetanus, diphtheria, and acellular pertussis
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Page 73.AMENDMENTS AND UPDAT ES
Amendment 
NumberDate SAP
Section(s) 
ChangedSummary of Amend ment(s) Reason
1 05 May 2022 6.1 
Inclusion 
CriteriaRemoved "age 18 years or older" from 
the inclusion criteriaTo allow  for enrollment of 
individuals who are <18 years of 
age as per CBER request given 
vaccine authorization/approval in 
younger ages.
9.1 Timing 
VariablesUpdated the definition of trimester sto 
≤13, 13.1 -≤26, 26To align with the definitions used 
for the study
11.3.1 
Major 
Congenital 
Malformati
onsUpdated formula for inverse probability 
weighting . Updated number of 
bootstrap samples from 10,000 to 200To fix an error and prevent 
negative values ; to align with the 
current method of using multiple 
imputation
Throughout 
documentFixed minor typos and references. To fix errors
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Page 8NOTE: In this document, any text taken directly from the Non- Interventional (NI) study 
protocol is italicized.
4.RATIONALE AND BACKGR OUND (SUMMARY)
Pfizer and BioNTech have partnered to develop a novel messenger ribonucleic acid (mRNA) 
vaccine (Candidate BNT162b2) against a novel coronavirus (severe acute respiratory  
syndrome coronavirus 2 [SARS -CoV -2])for the prevention of associated coronavirus disease 
2019 (COVID -19). TheUnited States Food and Drug Administration ( FDA) initially granted 
Emergency Use Authorization (EUA) for the Pfizer -BioNTech COVID -19 vaccine two- dose 
primary series on 11 December 2020 in individuals 16 years of age and older, and approved 
the vaccine for this population on 23 August 2021 ( FDA, 2021a ; FDA, 2021b ). FDA 
expanded the EUA on 10 May 2021 to include children 12 -15 years of age, and on 29 
October 2021 to include lower -dose vaccine administration for children 5 -11 years of age 
(FDA, 2021c ; FDA, 2021d ). The EUA was further amended on 12 August 2021 to include the 
administration of a third primary series dose in certain immunocompromised individuals 12 
years of age and older, and on 22 September 2021 to allow for use of a single booster dose at 
least six months after completion of the primary series in certain populations ( FDA, 2021e ).
Available data suggest that pregnant women who become infected with COVID -19 may be 
more likely to be hospitalized and may be at increased risk of preterm delivery ( MMWR, 
2020 ).Pfizer is conducting a Phase 2/3 clinical trial of the safety and immunogenicity of the 
Pfizer- BioNTech COVID -19 vaccine in pregnant women. While the current product labeling 
communicates that data are insufficient, the Pfizer- BioNTech COVID -19 vaccine may be 
received by pregnant women when they and their healthcare providers believe that 
risk/benefit considerations favor its use. As of 25 October 2021, more than 169,000 women 
reported to the Centers for Disease Control and Prevention’s (CDC) V -safe surveillance 
system that they were vaccinated during pregnancy ( CDC_2021a ).Therefore, information 
regarding the real -world safety of vaccination during pregnancy is essential from a public 
health perspective.
This observational study  described in the corresponding stud y protocol is being conducted to 
evaluate pregnancy  and infant safet y outcomes among pregnant women enrolled in an 
established North American pregnancy  registry  who were exposed to the Pfizer -BioNTech 
COVID -19 vaccine. This non -interventional study is designated as a Post- Authorization 
Safety Study (PASS) and is a postmarketing commitment (PMC) to the FDA.
This statistical analy sis pla n (SAP) provides a comprehensive and detailed description of 
statistical approaches and techniques to anal yze the data for the study .
5.RESEARCH QUESTION AND OBJECTIVE
Research Question: Is the risk of pregnancy and infant safety outcomes increased among 
pregnant women in the Organization of Teratology Information Specialists 
(OTIS)/MotherToBaby Pregnancy Registry (OTIS Pregnancy Registry) who were vaccinated 
with the Pfizer- BioNTech COVID -19 vaccine during pregnancy compared with those who 
did not receive an y COVID -19 vaccine during pregnancy?
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Page 9Study Objective
To assess whether pregnant women who received the Pfizer -BioNTech COVID -19 
vaccine during pregnancy experienced increased risk of pregnancy and infant safety 
outcomes, including major congenital malformations, spontaneous abortion, elective 
termination/abortion, stillbirth, preterm delivery, small for gestational age, and small 
for age postnatal growth at one year of age, relative to pregnant women who received
no COVID -19 vaccines during pregnancy. 
6.STUDY DESIGN (SUMMARY)
This proposed study  is a prospective, observational cohort study  of pregnancy  and infant 
safet y outcomes in pregnant women in the OTIS Pregnancy  Registry  who received the 
Pfizer -BioNTech COVID- 19 vaccine an y time from one month before the first day of the last 
menstrual period (LMP) to the end of pregnancy .The comparator cohort includes pregnant 
women who received no COVID -19 vaccines within one month before the first day  of LMP 
to end of preg nancy . The pregnancy outcomes are major congenital malformations, 
spontaneous abortion, elective termination/abortion, stillbirth, preterm delivery, and small 
for gestational age. The infant outcome is small for age postnatal growth at one year of age. 
Thetarget sample size for the study is 2000 pregnant women: 1100 pregnant women in the 
Pfizer- BioNTech COVID -19 vaccine exposure cohort and 900 pregnant women in the 
COVID -19 vaccine- unexposed comparator cohort .The main measures of effect are 
unadjusted and adjusted risk ratios (RRs) and 95% confidence intervals (CIs) comparing the 
Pfizer- BioNTech COVID -19 vaccine exposed cohort to the comparator cohort for the 
outcomes of major congenital malformations, small for gestational age, and postnatal 
growth; and u nadjusted and adjusted hazard ratios (HRs) and 95% CIs comparing the 
Pfizer- BioNTech COVID -19 vaccine exposed cohort to the comparator cohort for the 
outcomes of spontaneous abortion, elective termination/abortion, stillbirth, and preterm 
delivery .Seconda ry analy ses will be conducted to address the potential bias in prenatal 
diagnostic testing procedures to detect major congenital malformations performed prior to 
versus after enrollment, the separate effects of trimester of vaccine exposure for endpoints 
other than major congenital malformations, individual dose effects, potential bias in those 
who are lost to follow -up, and the effect of prior COVID -19 infection. Sensit ivity anal yses 
will be conducted to evaluate major congenital malformations identified in all pregnancies
including those not ending in at least one live birth , but excluding those lost to follow -up; in 
pregnancies with an y abnormal ultrasound findings pri or to enrollment; in pregnancies 
restrict edto those onl y those enrolled in the first trimester; and in an expand edcomparator 
group including those vaccinated with the Pfizer -BioNTech COVID -19 vaccine onl y in the 
second and/or third trimester. A sensitivi ty analy sis for the endpoint of preterm delivery  will 
be conducted stratified by those delivering following spontaneous labor versus labor 
induction or delivery  by cesarian section.
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Page 107.STUDY POPULATION ( SUMMARY)
7.1. Inclusion Criteria
Individuals must meet all of the following inclusion criteria to be eligible for inclusion in the 
study:
Residence in the US or Canada
Enrolled in the OTIS Pregnancy Registry and currently pregnant on or after 11 
December 2020 (i.e., date of EUA for the Pfizer -BioNTech COVID -19 vaccine)
7.2. Exclusion Criteria
Individuals meeting any of the following criteria will not be included in the study:
Previous entry into this study for a prior pregnancy
Receipt of any vaccine other than the Pfizer- BioNTech COVID -19 vaccine, influenza 
vaccine, or Tdap vaccine (e.g., Moderna or Johnson &  Johnson COVID -19 vaccines, 
human papillomavirus vaccine, hepatitis B vaccine, etc.) from one month before the 
first day of LMP up to and including end of pregnancy
Exposure to known human teratogens during pregn ancy within one month before the 
first day of LMP up to and including end of pregnancy
Known pregnancy outcome at time of study enrollment (e.g., positive prenatal 
diagnostic test results for a major congenital malformation prior to study entry)
7.3.Follow -Up
The study  entry  date, i.e., the follow -up start date, for pregnant women in the OTIS 
Pregnancy Registry is the study  enrollment date. Information is collected on their pregnancy 
to date and they are then followed for the duration of their pregnancy. In addition, infants 
will be followed for potential safety events through their first year of life .
Follow -up will end at the earliest of t he following events:
Lost to follow -up, i.e., an enrolled individual who withdraws or who fails to complete 
the outcome interview despite a standard number of telephone attempts and attempt 
to contact by mail as per study procedure manual within one year o f the participant’s 
estimated due date
Receipt of any vaccine other than the Pfizer- BioNTech COVID -19 vaccine, influenza 
vaccine, or Tdap vaccine (e.g., Moderna or Johnson &  Johnson COVID -19 vaccines, 
human papillomavirus vaccine, hepatitis B vaccine, etc. ) during pregnancy
Occurrence of spontaneous abortion, elective termination/abortion, or stillbirth
End of follow -up (i.e., one -year post -partum)
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Page 11End of study period
Infant death
Maternal death during pregnancy
8.STUDY SIZE
8.1.Sample Size
For the target sample size of 1800 participants enrolled in the study ,recruitment goals are 
set at 1100 participants in the Pfizer -BioNTech COVID -19 vaccine exposure cohort, and 900 
participants in the comparator cohort. The target sample size for the Pfi zer-BioNTech 
COVID -19 vaccine exposure cohort was increased from an initial sample size of 900 to 1100 
to allow for increased capture of women receiving a booster dose during pregnancy. The
rationale for the target sample sizes in each cohort was based on several considerations for 
feasibility of enrollment. These included early trends in referrals of COVID -19 vaccinated 
pregnant women to the OTIS Pregnancy Registry, combined with a reasonable time period 
for recruitment of pregnant women and the necessary time to collect outcome data to one 
year postpartum. An additional consideration was reasonable statistical power to detect 
differences for each outcome of interest. Balance in the cohort numbers by trimester of 
exposure in the vaccine -exposed cohort and by trimester of enrollment in both cohorts will be 
monitored on a monthly basis, and overall balance addressed by adjusting recruitment 
activities as needed. It is not possible to predict if the recruitment rates will be equal in all 
years, and therefore, sample size is based on estimates that may require revision as the study 
progresses.
As women will be eligible to enroll at any time in pregnancy, the gestational weeks at 
enrollment is expected to vary from 2 weeks to 41 weeks. Based on the gestational weeksat 
enrollment, only the portion of the overall sample enrolled prior to 20 weeks’ gestation will 
be eligible for the analysis of spontaneous abortion. We estimate based on prior experience 
that half the overall sample will enroll prior to 20 weeks. Simi larly, only the subset of the 
sample enrolled prior to 37 weeks’ gestation will be eligible for the analysis of preterm birth. 
It is estimated that 95% of the overall sample will enroll before 37 weeks. For the outcome of 
major congenital malformations , the main subset eligible for this assessment will be 
restricted in the exposed cohort to women who received at least one dose of the Pfizer -
BioNTech COVID -19 vaccine from one month prior to the first day of LMP to the end of the 
first trimester. Pregnant women who received the Pfizer- BioNTech COVID -19 vaccine only 
during their second or third trimester will be excluded from the analysis. Based on previous 
experience in OTIS studies, the estimated lost to follow- up rate is 5% ( Chambers et al, 2016 ).
8.2.Power Calculations
Based on these assumptions, for the outcome of major congenital anomalies , it is estimated 
that 85% will result in live birth after exclusion of pregnancy losses (10%) in women 
enrolled in the first half of pregn ancy, and lost -to-follow -up (5%). For spontaneous abortion, 
it is estimated that half of the overall sample will enroll prior to 20 weeks’ gestation. For 
preterm delivery, it is estimated that 80% of the overall sample will enroll prior to 37 weeks’ 
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Page 12gestat ion and will end in a singleton live birth. For the outcome of small for gestational age, 
it is estimated that 85% of the overall sample will end in a singleton live birth.
Baseline birth prevalence, incidence rates, and incidence proportions of major cong enital 
malformations, preterm delivery, small for gestational age, and small for age postnatal 
growth at one year of age ,respectively, are based on previous OTIS Pregnancy Registry 
studies and on general population data. Table 1 gives the power for variou s detectable 
relative risks (RRs)/hazard ratios (HRs) for two- sided alpha level of 0.05 in the comparisons 
of the exposed cohort to the comparator cohort for the range of background risks of the 
outcomes of interest.
Table 1.Sample Size and Power for a Specified Effect Size
Outcome N in Exposed 
CohortN in Comparator 
CohortBirth Prevalence/
Incidence in 
Comparator CohortDetectable 
Relative Risk/
Hazard RatioPower1
Major congenital 
malformations2311 765 3%32.1 65.8%
2.5 86.7%
2.7 92.6%
Spontaneous 
abortion550 450 10%41.5 66.6%
1.7 90.1%
1.8 95.6%
Preterm delivery 880 720 10%51.4 69.1%
1.5 85.6%
1.6 94.7%
Small for 
gestational age935 765 10%61.4 71.7%
1.5 87.6%
1.6 95.8%
Small for age 
postnatal growth 
at one year of age935 765 10%61.4 71.7%
1.5 87.6%
1.6 95.8%
1.Arcsine transformation using pwr.2p.test() in R package ‘pwr’ to obtain effect size h, where ℎ=2∗
−2∗     and p1= event rate in the exposed cohort, p 2= event rate in the 
comparison cohort, assuming 2 sided alpha = 0.05.
2.Among livebirths.
3.CDC, 2017. 
4.Avalos et al., 2012.
5.Ferre et al., 2016.
6.CDC, 2017; Nellhaus, 1968; Olsen et al., 2010.
NOTES
i.Major Congenital Malformations
N in exposed cohort for Major congenital malformations based on assumptions that 366 exposed 
to at least one dose from 1 month prior to LMP through the first trimester, and of these 10% will 
be lost to spontaneous abortion or stillbirth, and 5% lost to follow -up; 85% of the 366 enrolled 
will thus yield 311 eligible for the analysis.
N in comparator cohort = 900 enrolled x 85% resulting in at least one live birth = 765.
ii.Spontaneous Abortion
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Page 13Table 1.Sample Size and Power for a Specified Effect Size
Outcome N in Exposed 
CohortN in Comparator 
CohortBirth Prevalence/
Incidence in 
Comparator CohortDetectable 
Relative Risk/
Hazard RatioPower1
N in exposed cohort for spontaneous abortion based on estimate that ½ will be exposed and enroll 
in the first 20 weeks of gestation and thus be at risk of spontaneous abortion until 20 completed 
weeks; N of 1100 enrolled and exposed x 50% enrolled and exposed prior to 20 weeks = 550.
N in comparator cohort = 900 of which 50% will be enrolled prior to 20 weeks = 450.
iii.Preterm Delivery
N in exposed cohort based on 95% of the 1100 enrolled and exposed to at least one dose prior to 
37 weeks, 10% pregnancy loss, and 5% lost to follow -up for an overall estimated 80% eligible for 
the analysis; 1100 enrolled x 80% = 880.
N in comparator cohort based on same assumptions; 900 enrolled x 80% = 720.
iv.Small for Gestational Age
N in exposed cohort based on 1100 enrolled and exposed to at least one dose from 1 month prior 
to LMP up through the end of pregnancy, 10% pregnancy loss, and 5% lost -to-follow -up; 1100 x 
85% = 935.
N in comparator cohort based on same assumptions; 900 x 85% = 765.
v.Small for Age Postnatal Growth at One Year of Age
N in exposed cohort based on 1100 enrolled and exposed to at least one dose from 1 month prior 
to LMP up through the end of pregnancy; 10% pregnancy loss and 5% lost -to-follow -up; 1100 x 
85% =935.
N in comparator cohort based on same assumptions; 900 x 85% = 765.
9.DATA SOURCE (SUMMARY)
As part of the OTIS Pregnancy Registry protocol, data are collected using maternal 
interview(s) andmedical record review. To supplement the interim and pregnancy  outcome
interviews and toimprove recall, participants are given a pregnancy exposure diary to 
record any additional exposures (medications, vaccinations, vitamins, etc.) or events as the 
pregnancy progresses.
Data are recorded on hard copies of forms and these records are retaine d by OTIS at the 
OTIS Research Center. These forms are considered the primary data sources for studies and 
can be adapted to add new data elements. Data from these forms are extracted and entered 
into a customized OTIS study database.
9.1. Maternal Interviews
The maternal interviews are conducted by telephone at the intake/enrollment interview, then 
1-2 interim interviews (depending on gestational age of the pregnant woman at enrollment) ,
and lastly  the pregnancy  outcome interview. Data collected from each of th ese interviews 
include the following:
Intake/Enrollment Interview
oPregnancy history, including major congenital malformations, genetic 
disorders, number of live births, and multiple gestations
oCurrent health history
oPre-pregnancy weight and height
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Page 14oSocioeconomic and demographic information including maternal and 
paternal occupation, education and ethnicity
oIncome category
oAny COVID -19vaccine exposure prior to and during pregnancy , including 
dates, scheduled dose, and manufacturer
oVaccine use from one month prior to the first day of LMP and throughout 
pregnancy
oCurrent medication use, both prescription and over the counter
oOther environmental or occupational exposures
oAlcohol, tobacco, caffeine and illicit drug use
oCurrent pregnancy complications including illnesses
oFamily history of adverse pregnancy outcomes, including major congenital 
malformations and genetic disorders
oNames and addresses of health care providers
oCOVID -19 s ymptoms, treatments, and testing results
oReferral source
Interim Interview s I and II at 20-22 and 32-34 weeks’ gestation (if enrolled at those 
times)
oUpdate of data since last interview, including records of pregnancy exposures 
(medications, vaccinations, vitamins, supplements, and other prescription and 
over-the-counter product s), results of prenatal tests, events of interest ( e.g., 
pregnancy  complications, illnesses, pregnancy end prior to the expected due 
date), and contact info rmation
oCOVID -19 s ymptoms, treatments, and testing results
Pregnancy Outcome Interview at 0 to 6 wee ks after the expected due date (or at an 
interim interview point or earliest convenient time for the participant if pregnancy 
has ended)
oFor women with live born infants:
Date of delivery, hospital location and mode of delivery
Sex, birth weight, length an d head circumference
Apgar scores
Description of delivery or birth complications including 
malformations
Type and length of hospital stay for pregnant women and their infants
Delivering physician’s and infant physician’s names and addresses
Method of infant feeding
Pregnancy weight gain
COVID -19 s ymptoms, treatments, and testing results
Additional exposures and results of prenatal tests occurring since the 
previous interview
oFor women with spontaneous or elective abortions:
Date and type of outcome
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Page 15Hospital location if applicable
Prenatal diagnosis
Pathology results if available
COVID -19 s ymptoms, treatments, and testing results
Additional exposures and results of prenatal tests occurring since the 
previous interview
oFor women with stillborn infants:
All of the above for women with spontaneous or elective abortions
Sex
Delivery or birth complications including malformations
Birth size
Autopsy results if available
9.2.Medical Records and General Pediatric Evaluation
Medical records for pregnant women and t heir infants are captured at birth and again for 
the infant at one year of age to supplement information self- reported by the participant 
related to vaccine exposure, outcomes, prenatal tests, and medical history.
Medical records from the prenatal care pro vider, the hospital of delivery , any  specialty  
provider, and the pediatric care provider will be requested and abstracted for exposure, 
outcome and covariate/confounder data. A standard pediatric questionnaire will be completed 
by the ph ysician responsible for the care of each live born infant at or near one y ear of age. 
Data collected from medical records and the pediatric questionnaire include:
Exposure to Pfizer -BioNTech COVID -19 vaccine including dose number and dates;
Pregnancy  outcome;
Prenatal tests and results;
Pregnancy  complications;
Mode of delivery ;
Birth weight, length and head circumference of infant;
Apgar scores;
Length and ty pe of hospital stay ;
Major congenital malformations identified in the fetus or infant up through one y ear 
of age;
Postnatal growth measures for the infant up to one y ear of age (measurements 
between 9 to 15 months of age are considered valid; if multiple measurements are 
available, the evaluation ofweight, length and head circumference thatis closest to 
one y ear of age will be used ;
COVID -19 infection, testing and treatments.
To supplement maternal report of vaccination, a copy  of the COVID- 19 vaccine record is 
also requested from participants who have been vaccinated.
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Page 1610.VARIABLES
Variables for the exposures, outcomes, de mographics, and clinical characteristics of interest 
are included below. Data on these variables will be collected via maternal interview and 
medical record review per standard process described in the OTIS Pregnancy Registry 
protocol. Detailed operational definitions are provided below.
10.1. Timing Variables
The estimated date for the first day  of LMP isbased on maternal report or medical 
record . If the first day  of LMP and the menstrual cycle length are known, the first day  
of LMP is used to calculate the est imated date of confinement or due date. However, 
ifa firsttrimester ultrasound has been performed, and the estimated due date by  that 
ultrasound differ s by seven days or more from the first day  of LMP estimate, the first -
trimester ultrasound -derived date will be used. If there is no first trimester ultrasound, 
but an ultrasound performed in the second trimester has an estimated due date that 
diffe rs by14 day s or more, or a third trimester ultrasound estimated due date that
differs by 21 day s or more from the estimate b y first day  of LMP, the ultrasound -
derived date will be used. The earliest available ultrasound in pregnancy  is used to 
determine if an y adjustment in due date calculated by  first day  of LMP is necessary . 
When the first day  ofLMP and/or cy cle length areunknown or when a prenatal 
ultrasound estimates a gestational week that is discrepant according to obstetric 
guidelines, the due date calculated by  the earliest available ultrasound is used
(ACOG, 2017).
Weeks ’ gestation is defined as the number of weeks from the estimated first day  of 
LMP which is counted as day  0and calculated as:
(Current date – estimated date of the first day  of LMP )/7.
The definition of trimesters is as follows:
oFirst trimester: 30 day s prior to the first day  of LMP to ≤13 weeks’ gestation
oSecond trimester: 13 .1 weeks’ gestation to ≤ 26 weeks’ gestation
oThird trimester: 26 weeks’ gestation .
The start date for exposure ascertainment during pregnancy  is defined as one month 
prior to the first day  of LMP and calculated as the estimated date of the first day  of 
LMP minus 30 day s.
10.2. Identification of Exposure and Comparator
Vaccine exposure data are obtained by maternal report and/or medical record to classify 
Pfizer- BioNTech COVID -19 vaccine exposure status. The two sources of information are 
used in order to minimize misclassification of exposure status. Detailed informatio n 
regarding vaccine exposure status of participants is obtained through the maternal 
interviews including at enrollment, at interim timepoints during pregnancy, and at pregnancy 
outcome interview (0 to 6 weeks after the expected due date or end of pregnanc y). 
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Page 17Participants are directly queried about the specific vaccines they received, including 
information on the gestational timing, dates of exposure, and manufacturer . Vaccine 
exposures are coded using the Slone Drug Dictionary. Maternal report that a COVID -19 
vaccine was received is complemented by requesting a copy of the COVID -19 vaccine 
record. In addition, medical records from the obstetric provider, hospital of delivery, and 
any specialty provider are reviewed (when available) for all participants.
A participant is classified as unexposed if she reports that she did not receive any COVID -19 
vaccine and her medical record (when available) shows no indication that she received any 
COVID -19 vaccine. A participant is classified as exposed if she reports in the maternal 
interviews that she received the Pfizer -BioNTech COVID -19 vaccine or if there is supporting 
documentation in the medical record for receipt of the Pfizer- BioNTech COVID -19 vaccine. 
If maternal report indicates no receipt of a COVID- 19 vaccine but the medical record 
indicates discordance such that the Pfizer- BioNTech COVID -19 vaccine was administered, 
the medical record would supersede maternal report and the participant would be classified 
as Pfizer -BioNTech COVID -19 vaccine- exposed. Moreover, where maternal report indicates 
that the Pfizer- BioNTech COVID -19 vaccine was received but documentation in the medical 
record is discordant (i.e., no indication in medical record that COVID -19 vaccine was 
administered), the maternal report would supersede medical record for classification as 
exposed.
Table 2 below provides a description of variables for exposures to be included in this study. 
Each pregnancy and infant outcome will be analyzed separately, and the following exposure 
and comparator cohorts will be defined separately for each outcome analysis ( depending on 
a participant’s timing of vaccination/study enrollment as it relates to the at -risk period for an 
outcome ):
Pfizer -BioNTech COVID -19 V accine (Exposure)
–Receipt of at least one dose of the Pfi zer-BioNTech COVID -19 vaccine during 
the study period at any time from one month before the first day of LMP up to 
and including end of pregnancy
COV ID-19 Vaccine -Unexposed (Comparator)
–Receipt of no COVID -19 vaccines during the study period within one mo nth 
before the first day of LMP up to and including end of pregnancy
Table 2.Variables Related to Defining the Exposure, Comparator, Outcomes, 
Exclusions, and Date/Time
Variable Role Data source(s) Operational definition
Exposure to the 
Pfizer -
BioNTech 
COVID- 19 
vaccineExposure Maternal report
Vaccine record (e.g., 
COVID- 19 vaccine 
or yellow card)Maternal report ,vaccine record documentation, 
or medical record documentation of exposure to at 
least one dose of the Pfizer -BioNTech COVID -19 
vaccine any time from one month prior to first day 
of LMP to end of pregnancy.
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Page 18Table 2.Variables Related to Defining the Exposure, Comparator, Outcomes, 
Exclusions, and Date/Time
Variable Role Data source(s) Operational definition
Medical record
No COVID -19 
vaccine 
exposure during 
pregnancyComparator Maternal report
Medical recordMaternal report of no exposure to,as well as n o 
medical record documentation of ,any COVID -19
vaccines at any time from one month prior to first 
day of LMP to end of pregnancy
Weeks’ 
gestationTime Maternal report
Vaccine record (e.g., 
COVID -19 vaccine 
or yellow card)
Medical recordNumber of weeks (rounded to the nearest 0.1 
decimal )from the first day of LMP todate of 
interest calculated as:
(Date of interest –estimated date of
the first day of LMP ) / 7
The date of interest is based on maternal report , 
vaccine record, or medical record depending on 
which variable the date is for and which source 
was used to assign a value to that variable.
If the date of interest (e.g., vaccine exposure date) 
is in the 30 days prior to the first day of LMP, the 
gestational week would be between -0.1 and - 4.0.
Weeks’ 
gestationat time 
of receipt of the 
Pfizer -
BioNTech 
COVID -19 
vaccineTiming of 
exposureMaternal report
Vaccine record (e.g., 
COVID- 19 vaccine 
or yellow card)
Medical recordWeeks’ g estation (using calculation in row above)
for date of ‘Exposure to the Pfizer -BioNTech 
COVID -19 vaccine’ based on the vaccine dose
administration date from maternal report, vaccine 
record, or medical record
Weeks’ 
gestation at 
study 
enrollmentTiming of 
study 
enrollment,
ConfounderMaternal report
Medical recordWeeks’ g estation at time of study enrollment, 
continuous and categorical (<13, 13.1 -19.9, 
>20),
Trimester of 
Pfizer -
BioN Tech 
COVID- 19 
vaccin eTiming of 
exposure ,
ConfounderMaternal report
Vaccine record (e.g., 
COVID- 19 vaccine 
or yellow card)
Medical recordGestational week of vaccination by trimester 
catego ry:
1sttrimester defined as 30 days prior to first day 
ofLMP through 13.0 weeks’ gestation
2ndtrimester defined as 13.1 weeks ’ gestation
through 26.0 w eeks’ gestation
3rdtrimester defined as 26.1 weeks’ gestation to 
the end of pregnancy
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Page 19Table 2.Variables Related to Defining the Exposure, Comparator, Outcomes, 
Exclusions, and Date/Time
Variable Role Data source(s) Operational definition
Exposure to 
non-study 
vaccines during 
the pregnancy 
window up to 
study 
enrollmentExclusion 
criterionMaternal report
Vaccine record (e.g., 
COVID- 19 vaccine 
or yellow card)
Medical recordMaternal report of exposure to any vaccine other 
than the Pfizer -BioNTech COVID -19 vaccine, 
influenza vaccine, or Tdap vaccine (e.g., Moderna 
or Johnson &  Johnson COVID -19 vaccines, 
human papillomavirus vaccine, hepatitis B 
vaccine, etc.)
Maternal 
pregnancy 
exposure to a 
known human 
teratogenExclusion 
criterionMaternal report
Medical recordMaternal pregnancy exposure to a known human 
teratogen (e.g., Type I Diabetes ) (Annex 2: 
Table A-1)
Major 
congenital 
malformationPregnancy 
outcomeMaternal report
Medical record 
OTIS investigator 
reviewA major structural or chromosomal defect that 
has either cosmetic or functional significance to 
the child (e.g., a cleft lip). Classified using the 
CDC Metropolitan Atlanta Congenital Defects 
Program (MACDP) coding criteria ( CDC 2017 )
According to the CDC MACDP guidelines, the 
following do not qualify as major congenital 
malformations:
oThose findings that are present in infants 
with outcomes at <36 weeks gestational 
age or if gestational a ge is unavailable, 
weighing <2500 grams, and are 
attributed to prematurity alone, such as 
patent ductus arteriosus (PDA), patent
foramen ovale (PFO), and inguinal 
hernias
oInfants with only transient or infectious 
conditions, or biochemical abnormalities, 
are classified as being without major 
congenital malformations unless there is a 
possibility that the condition reflects an 
unrecognized major congenital 
malformation
An OTIS investigator also conducts a blinded 
review of medical records and maternal repor t 
to classi fyofmajor congenital malformations
Both sources of data are used to come to a 
final classification
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Page 20Table 2.Variables Related to Defining the Exposure, Comparator, Outcomes, 
Exclusions, and Date/Time
Variable Role Data source(s) Operational definition
Spontaneous 
abortionPregnancy 
outcomeMaternal report
Medical recordNon-deliberate embryonic or fetal death that 
occurs prior to 20 weeks’ gestation from first day 
ofLMP (Prager et al., 2021 )
Stillbirth Pregnancy 
outcomeMaternal report
Medical recordA non -deliberate fetal death that occurs at or 
after 20 weeks’ gestation from first day of LMP
but prior to delivery (CDC, 2021 (b) )
Preterm 
deliveryPregnancy 
outcomeMaternal report
Medical record A spontaneous or induced delivery at <37
gestational weeks from first day of LMP (CDC, 
2021(c) )
Small for 
gestational ageInfant 
outcomeMaternal report
Medical recordBirth size (weight, length, or head circumference) 
≤10thpercentile for sex and gestational age using 
NCHS pediatric growth curves for full term 
infants. Prenatal growth curves specific to 
preterm infants are used for preterm infants 
(Olsen et al., 2010 ); (Schlaudecker et al., 2017 )
Small for age 
postnatal 
growth at one 
year of ageInfant 
outcomeMedical record Postnatal size (weight, length or head 
circumference) ≤10thpercentile for sex and age 
using NCHS pediatric growth curves and adjusted 
postnatal age for preterm infants
Live birth Outcome -
specific 
inclusion/
exclusionMaternal report
Medical recordSingleton, twin or higher order gestation resulting 
in at least one live born infant
Abbreviations: CDC, Centers for Disease Control and Prevention; LMP, last menstrual period; MACDP, 
Metropolitan Atlanta Congenital Defects Program; NCHS, National Center for Health Statistics; OTIS, 
Organization of Teratology Information Specialists; US, United States.
10.3. Classification of Pregnancy and Infant Outcomes
The following pregnancy and infant outcome variables (refer to Table 2) are obtained by 
maternal report and/or medical record review (when available) as part of existing 
procedures for the pregnancy registry.
10.3.1. Major Congenital Malformations
Defined for pregnancies ending with at least one live born infant as a defect that has 
either cosmetic or functional significance to the child (e.g., a cleft lip) diagnosed 
during pregnancy up to 1 year of age as reported by participants/ healthcare 
providers or identified through medical record review.
A pregnancy  with multiple births is counted as one malformed outcome if one or 
more of the infants/fetuses are malformed.
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Page 21Classification of major defects is performed uniformly across cohorts according to 
the CDC Metropolitan Atla nta Congenital Defects Program (MACDP) coding 
criteria ( CDC, 2017 ).
oSome major congenital malformations, such as club foot or cranial synostosis, 
could be due to position of the infant in the uterus or could be primary defects 
initiated earlier in pregnancy. In most cases, it is not possible to know the true 
onset or etiology of the defect. Therefore, using CDC coding criteria, these 
anomalies are counted as major congenital malformations uniformly across 
all cohorts.
oOne except ion to using the CDC coding criteria is that chromosomal 
anomalies will not be counted as major congenital malformations as it is 
unlikely that a vaccine exposure could cause a chromosomal defect.
The uniform coding reduces differences in outcome definitio ns between studies for a 
better interpretation of results in the event they are compared. It is anticipated that 
the occurrence of defects that are unrelated to vaccine exposure in the proposed 
study population will be nondifferential across cohorts. There fore, their inclusion, 
when indicated, represents part of the baseline risk for major congenital 
malformations in each cohort. This should not impact the risk estimates and measures 
of association. 
Major congenital malformations identified by prenatal ult rasound or examination of 
the products of conception following elective termination/abortion or spontaneous 
abortion will not be included in the primary analysis due to potential bias involved in 
non-uniform use of prenatal diagnosis and pathology evaluati on for all abortuses; 
however, these defects will be considered in a sensitivity analysis including all defects 
in the numerator over all pregnancies with known outcome in the denominator 
(excluding lost to follow -up).
As per recommendations in the FDA dra ft Guidance for Industry Postapproval 
Pregnancy Safety Studies (May 2019), an expert dysmorphologist and co- investigator 
for OTIS Pregnancy Registry studies, Dr. Kenneth Lyons Jones, reviews all the 
medical records and reports of major congenital malformat ions. The review is done 
blinded to exposure status and performed in the same manner for exposed and 
comparator cohorts. If the major congenital malformation diagnosis is determined to 
be incorrect (e.g., misdiagnosed or another ty pe of defect), the review er reclassifies 
the outcome, the change is documented in the database, and the rationale for the 
change is also documented. In cases where classification is not clear, consultation 
with the Medical Director of Metropolitan Atlanta Congenital Defects Progra m 
(MACDP )is available, as well as expert consultation from the study  Scientific 
Advisory  Board. Through this adjudication process a consensus classification is 
achieved.
Independent confirmation of certain defects is required via medical record review. 
For example, a heart murmur thought to represent a ventricular septal defect prior to 
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Page 221 year of age will be included if it is confirmed as a heart defect by a diagnostic 
procedure such as cardiac ultrasound. Similarly, a midline cutaneous marker at L2 -
L3 not ed will be included as occult spinal dysraphism only if confirmed by 
appropriate imaging studies.
10.3.2. Spontaneous abortion
Defined as non- deliberate embry onic/fetal death (miscarriage) which occurs prior to 20 
weeks’ gestation. In pregnancies involving multipl es with one or more of the outcomes 
ending in spontaneous abortion, when there are no live births, the pregnancy is counted as 
one spontaneous abortion event; however, when the pregnancy ends in at least one live -born 
infant, the pregnancy  is counted as a live birth outcome.
10.3.3. Elective termination/abortion
Defined as deliberate termination of pregnancy at any time in gestation. Reasons for elective 
termination/abortion are captured and are classified as due to medical reasons or social 
reasons.
10.3.4. Stillbirth
Defined as non-deliberate fetal death any time in gestation at or after 20 weeks’ gestation. In 
pregnancies involving multiples with one or more of the outcomes ending in stillbirth, when 
there are no live births, the pregnancy  is counted as one stillbirth ev ent; however, when the 
pregnancy  ends in at least one live -born infant, the pregnancy  is counted as a live birth.
10.3.5. Preterm delivery
Defined as live birth prior to 37 weeks’ gestation.
10.3.6. Small for gestational age at birth
Defined separately for weight, length, and head circumference (binary endpoints) asbirth 
sizeless than or equal to the 10th centile for sex and gestational age using National Center 
for Health Statistics (NCHS) standard pediatric growth curves for full term or preterm 
infants ( CDC, 2000 ).Prenatal growth curves specific to preterm infants will be used for 
premature infants ( Olsen et al., 2010 ).
10.3.7. Small for age postnatal growth at one year of age
Defined separately for weight, length, and head circumference (binary endpoints) as 
postnatal size less than or equal to the 10th centile for sex and age using NCHS pediatric 
growth curves ( CDC, 2000) , and adjusted chronological age for preterm infants if the 
postnatal measurement is obtained at less than 1 year of age ( CDC, 2000 ).The 
measurements obtained closest to one y ear of age, and within three months prior to or after 
one y ear of age (9- 15 months) are used. 
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Page 2310.4. Demographic and Clinical Charac teristics
Potential confounders and other covariates to be collected include maternal age, 
race/ethnicity, socioeconomic status, pregnancy and health history, lifestyle factors, 
comorbidities, medication, vaccine and vitamin/mineral exposures, and prenatal tests. 
Table3 provides a description of corresponding variables to be included in this study.
Table 3.Demographic and Clinical Variables
Variable Role Data source(s) Operational definition
Age Confounder Maternal report Maternal age (years) at due date, continuous 
and categorical (<25, 25 -29, 30- 34, >34)
Race Confounder Maternal report Maternal/paternal race (Caucasian/White, 
Black, Asian/Pacific Islander, Native 
American, Other)
Ethnicity Confounder Maternal report Maternal/paternal ethnicity (Hispanic, Non -
Hispanic)
Education Confounder Maternal report Maternal educational c ategory (years of 
completed education <12, 12 -15, >15)
Socioeconomic 
categoryConfounder Maternal report Hollingshead Socioeconomic Status (SES)
based on maternal and paternal occupation 
and education (Categorical: high 1 -2, 
moderate 3; low  4-5)(Hollingshead, 1975 )
Geographic area of 
residenceConfounder Maternal report Geographic area of residence (US, Canada)
Referral source Confounder Maternal report Source options: Sponsor, OTIS service, health 
care provider (HCP), Internet, Referrals from 
other University of California Medical 
Centers , Other
Height Confounder Maternal report Maternal height in centimeters (cm)
Pre-pregnancy body 
weightConfounder Maternal report
Medical recordMaternal pre -pregnancy body weight in 
kilograms (kg)
Pre-pregnancy body 
mass index (BMI)Confounder Maternal report Calculated as maternal pre- pregnancy body 
weight in kilograms (kg) divided by maternal 
height in meters squared (m2). Categorized as:
Underw eight = <18.5 kg/m2
Normal weight = 18.5-24.9 kg/m2
Overweight = 25-29.9 kg/m2
Obese = ≥30kg/m2
Number of prior 
pregnanciesConfounder Maternal report
Medical recordNumber of times ever pregnant prior to 
current pregnancy (1, 2-3, 4-5, ≥6)
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Page 24Table 3.Demographic and Clinical Variables
Variable Role Data source(s) Operational definition
Number of previous 
live birth or stillbirth 
deliveriesConfounder Maternal report
Medical recordNumber of previous live birth or stillbirth 
deliveries , i.e., parity defined as number of 
previous pregnancies ending in a live or 
stillbirth after 24 w eeks’ gestation (0, 1-2, 3-4, 
≥5)
Previous pregnancies 
with a major 
congenital 
malformation Confounder Maternal report ≥1 prev ious pregnancy with a major 
structural or chromosomal defect diagnosed 
in utero or post -partum –Yes/No
Type of major 
congenital 
malformation in 
previous pregnanciesConfounder Maternal report Specific major structural or chromosomal 
defect in previous pregnancies that has either 
cosmetic or functional significance to the 
child (e.g., a cleft lip) classified using CDC 
coding criteria
Number of previous 
pregnancies ending in 
spontaneous abortionConfounder Maternal report
Medical recordNumber of previous pregnancies ending in 
spontaneous abortion (0, 1, 2, ≥3)
Number of previous 
pregnancies ending in 
elective 
termination/abortionConfounder Maternal report
Medical recordNumber of previous pregnancies ending in 
elective termination/abo rtion (0, 1, 2, ≥3)
Previous pregnancies 
ending in preterm 
deliveryConfounder Maternal report ≥1 previous pregnancy ending in preterm 
delivery –Yes/No
Previous pregnancies 
ending in fetal growth 
restrictionConfounder Maternal report ≥1 previous pregnancy ending in fetal growth 
restriction –Yes/No
Number of previous 
ectopic pregnanciesConfounder Maternal report
Medical recordNumber of previous pregnancies ending in 
ectopic pregnancy (0, 1, 2, ≥3); ectopic 
pregnancy is defined as a pregnancy in which 
the fetus develops outside the uterus, typically 
in a fallopian tube
Family history of 
genetic disorders and 
major congenital 
malformationsConfounder Maternal report Any family history of a major structural or 
chromosomal defect that has either cosmetic 
or functional significance to the child as 
defined using the CDC coding criteria –
Yes/No
Prenatal vitamin, 
multivitamin, or folic 
acid use in pregnancyConfounder Maternal report Prenatal, multivitamin, or folic acid 
supplement use by timing (be gan prior to 
conception, post -conception only, not taken at 
all)
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Page 25Table 3.Demographic and Clinical Variables
Variable Role Data source(s) Operational definition
Alcohol use in 
pregnancyConfounder Maternal report Light or moderate alcohol use based on an 
average dose and frequency . Participants are 
classified in this group if they have had any 
amount of alc ohol in pregnan cy but have not 
exceeded >14 drinks per week for 4 or more 
weeks after conception. –Yes/No (heavy 
alcohol use is classified as a human teratogen 
which is exclusionary, thus no participants in 
the study would have heavy use)
Tobacco use in 
pregnancyConfounder Maternal report Any tobacco use during pregnancy –Yes/No
Prenatal diagnostic 
tests prior to study 
enrollmentConfounder Maternal report
Medical record≥1diagnostic tests performed during 
pregnancy prior to study enrollment 
(Ultrasound level 1, Ultrasound level 2, 
Chorionic Villus Sampling, and
Amniocentesis)
Prenatal diagnostic 
tests any time during 
pregnancyConfounder Maternal report
Medical record≥1diagnostic tests performed any time in 
pregnancy (Ultrasound level 1, Ultrasound 
level 2, Chorionic Villus Sampling, and
Amniocentesis)
Pregnancy 
complicationsConfounder
or Mediator Maternal report
Medical recordPregnancy induced hypertension –Yes/No
Preeclampsia –Yes/No
Gestational diabetes –Yes/No
Each pregnancy complication will be 
considered as a confounder for the endpoints
of preterm delivery, small for gestational age 
at birth, and small for age postnatal growth at 
one year of age. If the complication occurs 
after exposure to the Pfizer -BioNTech 
COVID -19 vaccine in pregnancy , the 
complication will also be evaluated as a 
potential mediator of those same endpoints
Comorbid maternal 
medical historyConfounder Maternal report
Medical recordComorbid maternal medical history current 
diagnosis in pregnancy:
Chronic hypertension –Yes/No
Asthma –Yes/No
Psychiatric disorder –Yes/No
Immune disorders –Yes/No
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Page 26Table 3.Demographic and Clinical Variables
Variable Role Data source(s) Operational definition
Current medication 
useConfounder Maternal report Prescription and over -the-counter 
medications are captured for the period of 
time from the first day of LMP through the 
end of pregnancy. Dose, frequency, duration, 
and indication including stop and start dates 
are collected ; specific categories of 
medication treatments in pregnancy :
Antihypertensive medications – Yes/No
Asthma medications –Yes/No
Psychotherapeutic medications –Yes/No
Immune modulators –Yes/No
Exposure to the 
influenza or Tdap 
vaccineConfounder Maternal report
Medical recordExposure to an influenza or Tdap vaccine any 
time from one month prior to first day of LMP 
up to and including end of pregnancy
COVID- 19 vaccine 
prior to pregnancyConfounder Maternal report
Medical recordExposure to at least one dose of any COVID -
19 vaccine any time prior to one month before 
the first day of LMP
COVID -19 symptoms 
during pregnancyConfounder Maternal report Symptom inventory ( Annex 2: Table A -2)
COVID- 19 infection 
positive test during 
pregnancyConfounder Maternal report
Medical recordTest results positive for COVID -19(e.g., viral 
RNA/PCR) from maternal report or medical 
record
COVID- 19 infection 
positive test prior to 
pregnancyConfounder Maternal report
Medical recordTest results positive for COVID -19 (e.g.,viral 
RNA/PCR) from maternal report ormedical 
record
Abbreviations: BMI, body mass index; CDC, Centers for Disease Control and Prevention; 
cm, centimeters; kg, kilograms; HCP, health care provider; LMP, last menstrual period; 
OTIS, Organization of Teratology Information Specialists; PCR, polymerase chain r eaction; RNA, 
ribonucleic acid .
11.MISSING DATA
Multiple imputation (MI) will be conducted to handle the missing data. Missing values 
typically occur in less than 5% of the cases for any single covariate based on prior 
experience (Chambers, et al., 2019). They are assumed to be missing at random. When there 
are missing values in any of the selected confounders, multiple imputation (MI) will be 
conducted, using the R package MICE (multivariate imputation by chained equations) (van 
Buuren S and Groothuis -Oudshoorn K, 2011) . Demographic information, pregnancy history, 
information about current pregnancy, and concurrent diseases will be used as possible 
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Page 27‘predictors’ in MICE. The generalized R2will be used as a measure of correlations between 
each ‘target’ (i.e., the variable to be imputed) and a predictor. If the value of R (i.e., square 
root of R2) is over 0.1, the variable will be retained as a predictor. Predictors with strong 
collinearity might be excluded (for example, one of race and ethnicit y, and one of gravidity 
and parity). Although each outcome within each cohort comparison has its unique set of 
participants, MI is conducted for missing data using the entire dataset, i.e., on all cohorts 
combined.
For the outcome of spontaneous abortion, for some cases the exact date of the event might be 
unknown, and instead a window for possible spontaneous abortion time is available. This is 
known as interval censored data, and can also be handled using MI (Pan, 2000) An exact 
spontaneous abortion time w ill be imputed by sampling uniformly from the corresponding 
time window. 
The number of above imputations will be 10, i.e., 10 datasets with imputed data will be 
created. Each imputed data set gives a point estimate of the regression coefficients as well as 
its standard deviation, which will be combined across the 10 datasets to obtain the final 
estimate of the causal RR/HR and their 95% CI’s (Little and Rubin , 2002).
12.STATISTICAL METHODS AND DATA ANALYSIS
12.1. Data Cleaning and Preparation of Datasets
The origi nal data will be cleaned and validated b y the OTI S Data Manager and exported in 
the form of multiple datasets to the study  statisticians. A checklist will be filled out and 
reviewed prior to the analy sis to ensure the original data have been properly  valid ated and 
meet the study  criteria. There will be close communications between the statisticians and the 
OTIS Research Manager during this process. Based on the original data, the statisticians 
derive variables to be used for the analy ses as described in the definitions of the variables in 
Table 2 and Table 3.
12.2. Demographic and Baseline Characteristics
The distributions of demographic and baseline characteristics will be summarized within 
each exposure cohort. Continuous variables will be summarized using the following 
statistics: mean, standard deviation, minimum, 1st quartile, median, 3rd quartile, and 
maximum. All categorical variables will be summarized using counts and percentages. 
Missing data or unknown responses will not be counted in the perc entages.
12.3. Primary Analyses
The following measures will be calculated for the pregnancy and infant outcomes: birth 
prevalence of major congenital malformations; incidence rates of spontaneous abortion, 
elective termination/abortion, stillbirth, and preterm delivery; and incidence proportions of 
small for gestational age and small for age postnatal growth at one year of age. For each 
outcome, risk estimates will be described separately for the Pfizer -BioNTech COVID -19 
vaccine exposure cohort and the comparator cohort . The outcomes will be compared
between the Pfizer- BioNTech COVID -19 vaccine -exposed cohort and the comparator cohort.
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Page 28Where feasible, comparisons will also be made using methods to control potential 
confounding.
The eligible populations and time pe riods for analyses may differ by pregnancy outcome 
depending on a participant’s exposure status, timing of vaccine exposure/study enrollment as 
it relates to the at -risk period for an outcome, in addition to type of birth ( Table 4) . The 
denominators for each exposure/comparator cohort and outcome analysis will include 
participants as follows:
Table 4.Denominators for Outcomes by Exposure/Comparator Cohort
Outcome Pfizer -BioNTech COVID -19 
Vaccine -Exposed
(Exposure)COVID -19 Vaccine -
Unexposed
(Comparator)
Major congenital 
malformationsParticipants who received the 
Pfizer- BioNTech COVID -19 
vaccine (1st, 2nd, 3rd, or booster
dose) any time from one month 
before the first day of LMP 
through their first trimester and 
whose pregnancy resulted in >1 
live birthParticipants who did not receive 
any COVID -19 vaccines any 
time from one month before the 
first day of LMP up to and 
including end of pregnancy and 
whose pregnancy resulted in >1 
live birth
Spontaneous 
abortionParticipants who received the 
Pfizer- BioNTech COVID -19 
vaccine (1st, 2nd, 3rd, or booster 
dose) any time from one month 
before the first day of LMP up 
to 20 weeks’ gestation and were 
enrolled in the study prior to 20 
weeks’ gestationParticipants who did not receive 
any COVID -19 vaccines any 
time from one month before the 
first day of LMP up to and 
including end of pregnancy and 
were enrolled in the study prior 
to 20 weeks’ gestation
Elective 
termination/abortionParticipants who received the 
Pfizer- BioNTech COVID -19 
vaccine (1st, 2nd, 3rd,or booster
dose) any time from one month 
before the first day of LMP up 
to and including end of 
pregnancyParticipants who did n ot receive 
any COVID -19 any time from 
one month before the first day of 
LMP up to and including end of 
pregnancy
Stillbirth Participants who received the 
Pfizer- BioNTech COVID -19 
vaccine (1st, 2nd, 3rd, or booster 
dose) any time from one month 
before the first day of LMP up Participants who did not receive 
any COVID -19 vaccines any 
time from one month before the 
first day of LMP up to and 
including end of pregnancy, but 
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Page 29Table 4.Denominators for Outcomes by Exposure/Comparator Cohort
Outcome Pfizer -BioNTech COVID -19 
Vaccine -Exposed
(Exposure)COVID -19 Vaccine -
Unexposed
(Comparator)
to and including end of 
pregnancy, but must have 
follow -up at or after 20 weeks’ 
gestationmust have follow- up at or after 
20 weeks’ gestation
Preterm delivery Participants who received the 
Pfizer- BioNTech COVID -19 
vaccine (1st, 2nd, 3rd, or booster 
dose) any time from one month 
before the first day of LMP up 
to 37 weeks’ gestation, were 
enrolled in the study prior to 37 
weeks’ gestation, and whose 
pregnancy resulted in a live-
born singletonParticipants who did not receive 
any COVID -19 vaccines any 
time from one month before the 
first day of LMP up to and 
including end of pregnancy, 
were en rolled in the study prior 
to 37 weeks’ gestation, and 
whose pregnancy resulted in a 
live-born singleton
Small for gestational 
ageParticipants who received the 
Pfizer- BioNTech COVID -19 
vaccine (1st, 2nd, 3rd, or booster 
dose) any time from one month 
before the first day of LMP up 
to and including end of 
pregnancy and whose 
pregnancy resulted in a live-
born singletonParticipants who did not receive 
any COVID -19 vaccines any 
time from one month before the 
first day of LMP up t o and 
including end of pregnancy and 
whose pregnancy resulted in a 
live-born singleton
Small for age 
postnatal growth at 
one year of ageParticipants who received the 
Pfizer- BioNTech COVID -19 
vaccine (1st, 2nd, 3rd, or booster 
dose) any time from one month 
before the first day of LMP up 
to and including end of 
pregnancy and whose 
pregnancy resulted in a live-
born singletonParticipants who did not receive 
any COVID -19 vaccines any 
time from one month before the 
first day of LMP up t o and 
including end of pregnancy and 
whose pregnancy resulted in a 
live-born singleton
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Page 3012.3.1. Major Congenital Malformation
For the endpoint of major congenital malformations, the exposure of interest is at least one 
dose of the Pfizer -BioNTech COVID -19 vaccine during the first trimester. The primary  
comparison will be the birth prevalence o f major congenital malformations between the 
exposed cohort and the comparator cohort among pregnancies resulting in at least one live 
born infant .Thebirth prevalence of ma jor congenital malformations will be calculated for 
each cohort as the number of pregnancies ending in at least one liveborn infant with a major 
congenital malformation divided by  the number of all pregnancies for women in the cohort 
ending in at least one live born infant (Table 4), multiplied by  100. A point estimate of the 
crude (i.e., unadjusted) risk ratio (RR) of the exposed cohort versus the comparison cohort, 
as well as its 95% confidence interval (CI), will be computed using normal approximation 
method. When the expected frequency of any of the cells of the contingency table is less than 
five, the CI will be obtained by an exact method using the software StatXact. The method is 
based on inverting an unconditional exact hy pothesis test (Agresti and Min, 2001).
Due to the observational nature of the study, the above crude estimate of RR will be adjusted 
for potential confounders (Rosenbaum, 2002 ), provided that there are sufficient number of 
events. A list of potential confounders will be provided in a separate appendix to the SAP for 
each outcome prior to the final analysis, based on scientific knowledge including literature 
review. In addition, all of the following three criteria will be applied in accordance with the 
definition of confounders ( Greenland et al., 1999 ; Xu et al., 2018 ):
1) by assessi ng each considered variable in a logistic regression model containing the 
exposure variable and the outcome variable to determine if inclusion of that single covariate 
changes the estimate of the odds ratio (OR) for exposure by 10% or more: |OR 2–OR 1|/OR 1
≥ 10% where OR 1is the crude OR and OR 2is the OR adjusting for the covariate in question;
2) standardized mean differences ( SMD) greater than 0.1;
3) association with the outcome with p -value < 0.2 in the unexposed cohort (using chi -square 
test or two sample t- test). Care will be taken not to include those variables that are strongly 
associated with the exposure variable but only weakly associated with the outcome variable 
(e.g, instrument -like variables )(Brookhart et al., 2006).
The confounders identified above will be used to build the propensity score for exposure 
(Rosenbaum, 2002 ). R package ‘twang’ or similar R package available at the time of 
analysis will be used for this purpose, follo wing which SMD will be used to check the 
balance of the covariates between the cohorts.
The primary  anal ysis will estimate the effect of exposure on the risk for major structural 
defect as the causal risk ratio ( Hernán and Robins, 2020) using inverse probability of 
treatment weighting (IPTW) .The causal risk ratio is defined as (= 1)/ P(= 1) , 
where is the potential outcome under exposure and is the potential outcome 
without exposure . The risks for the potential outcomes will be estimated using the inverse 
probability  weighting:
(= 1) = ∑(1 −  ), (= 1) = ∑,
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Page 31here and denote the observed outcome ( = 1or 0for presence or absence of a major 
congenital malformation) and exposure status ( = 1or 0for exposed or unexposed) among 
the  pregnancies, and is the inverse of the probability  of being in the observed exposure 
group estimated using the propensity  score, which has been stabilized and further trimmed to 
be between 0.1 and 10 if necessary (Austin and Stuart, 2015 ). The causal risk ratio is then 
estimated by  (= 1)/ (= 1) . The 95% CI s will be obtained using the bootstrap 
estimated variance and asy mptotic normality , with 200 bootstrap samples, i.e., resampling 
with replacement on the pregnant women. The propensity  score will be re -computed for each 
bootstrap sample to accou nt for variability  in the estimation of the weights.
Provided there are sufficient number of events, i.e.,at least 10 events per parameter in the 
regression model, an additional analy sis will be conducted using outcome regression (Xu et 
al., 2018 ; Vansteelandt and Daniel, 2014 ). Alogistic regression model will be fitted with 
major congenital malformation (Y) as the outcome, and exposure (A) and propensity score 
(L) as regressors. Outcomes regression tends to be more stable and efficient than IP TW 
especially given the expected rare number of events ( Xu et al., 2018 ), and has known robust 
properties against model misspecification ( Vansteelandt and Daniel, 2014). In a second step, 
standardization will be performed to obtain the estimated causal risk ratio (Hernán and 
Robins, 2020), which has the interpretation as the marginal or population averaged risk ratio. 
Note that 
(= 1)=∑( = 1 | = 1,  =  )( =  ) .
The above can be estimated by  first predicting the potential outcomes (=
1| = 1,  =  )= ( = 1 | = 1,  =  ), using the fitted outcomes regression model for 
the whole sample (i.e., both exposed and unexposed), assu ming that their treatments are all a 
= 1. (= 1) will be estimated by averaging these predicted values over the distribution 
of L, as in the equation above. P (= 1)is estimated in a similar way . Finally, the causal 
risk ratio will be estimated by dividing these two estimated probabilities . The CI’s are 
obtained by  bootstrap with 200bootstrap samples, i.e. resampling with replacement of the 
pregnant women.
12.3.2. Spontaneous Abortion, Stillbirth, and Preterm Delivery
The analyses of spontaneous abortion, stillbirth, and preterm delivery are complicated by 
several factors based on the timing of stud y entr y and the at -risk period for the outcome. The 
eligible populations and time periods for the anal yses of each of these outcomes are as 
follows:
Spontaneous abortion: Only those women who are enrolled prior to 20.0 weeks of 
gestation in both exposed and comparator cohorts, and only  those women exposed to 
at least one dose of th e Pfizer -BioNTech COVID- 9 vaccine from 30 day s before the 
first day  ofLMP up to 20.0 weeks’ gestation.
Stillbirth: Only  those pregnancies that reach at least 20 weeks of gestation are eligible 
for anal ysis.
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Page 32Preterm delivery : Only those women exposed to at least one dose of the Pfizer-
BioNTech COVID -19 vaccine, or enrolled in the study for unvaccinated comparator, 
prior to 37 weeks’ gestation and whose pregnancies resulted in a live -born singleton; 
pregnancies with twins or higher order multiples will be ex cluded.
Because women can enter the study at arbitrary times in gestation (i.e., left truncation ), 
participants are not followed from gestational age zero. Those who experience the event 
prior to enrollment will never enter the stud y, leading to left truncation of the time to event. 
This can produce selection bias if earl y vaccination time causes earl y time to event. The 
event time is also right -censored whenever a subject is lost to follow- up prior to observing 
the outcome. In addition, vaccine exposu re can occur prior to or throughout enrollment, so 
exposure status is time -dependent . In order to address these issues, survival analysis methods 
will be used to handle possible left truncation, right- censoring, and time -dependent exposure 
or confounding. The Cox proportional hazards marginal structural model (MSM) 
incorporating time -dependent vaccine exposure and relevant covariates will be used to 
estimate the causal hazard ratio (HR) and 95% CIs for exposure to the Pfizer- BioNTech 
COVID -19 vaccine (Hernán et al, 2001). For  ≥ 0 let () be an indicator for exposure to 
the Pfizer -BioNTech COVID- 19 vaccine b y time during the exposure window and let 
denote the potential time to spontaneous abortion had a subject followe d the exposure profile 
. The marginal structural model is:
()=  ()exp(())
where ()is the hazard of at time , is the baseline hazard function representing the 
risk for a subject who never receives the vaccine, and exp()is the causal relative risk for 
the effect of exposure.
The method that will be used to estimate the MSM depends on whether there are time -
dependent confounders that are also affected by previous exposure to the Pfizer -BioNTech 
COVID -19 vaccine ( Hernán et al, 2001). This study  considers two potential sources of time-
dependent confounding: COVID -19 circulation season and COVID- 19 infection in 
pregnancy  prior to vaccination . Circulation season is an external mechanism that is n ot 
affected b y a subject’s previous vaccine exposure . On the other hand, infection during 
pregnancy  is likel y to be affected b y previous vaccine exposure . The estimation method 
therefore depends on whether infection is included as a confounder .
If infecti on during pregnancy  is not selected as a confounder, the MSM can be consistently  
estimated using multivariable regression. In this approach, a time -dependent proportional 
hazards model for the time to spontaneous abortion will be fit, with effects for the time-
varying exposure as well as all selected confounders. The usual 95% Wald confidence 
intervals will be computed using the standard software.
If infection during pregnancy  is selected as a confounder, the MSM can be consistently  
estimated using IPTW . To obtain the weights, a proportional hazards model is fit for the time 
to vaccine exposure during the exposure window, adjusting for the selected confounders (Xu 
et al., 2014 ; Yang et al., 2018 ). Estim ates of the conditional survival function (|) and 
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Page 33density  function (|) given the confounders are then used to compute time-dependent 
propensity  scores and weights . At a fixed time , the weight for a woman with confounders 
() who is sti ll at risk for SAB b y time is ()= 1/ (), where ()is computed as 
follows:
1)For a subject who is not exposed during the window,
() = (| ())if they  have not been fully  vaccinated prior to the window
() = 1 if they  have been full yvaccinated prior to the window
2) For a subject who is exposed during the window at time ,
() = (| ()) if < 
(|( )if ≥ 
When there is a strong association between confounders and exposure time, the weights can 
be large for some subjects, leading to a large variance in the IPTW estimator. Variabilit y can 
be reduced using stabilization and trimming ( Austin and Stuart, 2015). The weights will be 
stabilized by  multiply ing by  (), which is computed analogous to ()except using the 
baseline quantities ()= (|0)and ()= (|0) (Yang et al., 2018) If necessary , the 
weights will be further trimmed to lie between 0.1 and 10.
The exposure time is not observed for women who never enter the stud y due to left 
truncation of the outcome. As a consequence, the exposure time may  also be subject to left 
truncation. This is a potential source of bias in the PS estimates, and a possible limitation of 
the IPTW method.
The standard er rorse()of the causal exposure effect will be estimated using the 
nonparametric bootstrap, and 95% CIs will be computed as ± 1. 96se().
12.3.3. Elective Termination/Abortion
The analysis of elective termination/abortion will be descriptive as the number of e vents is 
expected to be low. 
12.3.4. Small for Gestational Age at Birth and Small for Age Postnatal Growth at One 
Year of Age
The following are binary endpoints: small for gestational age at birth in weight, length, and 
head circumference; and small for age postnatal growth at one year of age 10thcentile in 
weight, length, and head circumference. The analysis of the incidence proportion of infants 
with each of these outcomes will be similar to the analysis of the outcome major congenital 
malformations (see Section 10.3.1 . “Major Congenital Malformation) and will be restricted 
to pregnancies ending in a live born singleton; pregnancies with twins or higher order 
multiples will be excluded . For these outcomes, exposure to any dose of the Pfizer-BioNTech 
COVID -19 vaccine in any trimester will be compared to the unexposed cohort.
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Page 3412.4. Secondary Analyses
12.4.1. Stratified/Subgroup Analyses
For the endpoint of major congenital malformations, the comparison will also be carried out 
within each of two strata, according to whether the participant had prenatal diagnostic 
testing, such as level 2 ultrasound, amniocentesis or chorionic villus sampling, pri or to 
enrollment in the study or not.
Instratified analyses, the separate effects of vaccine exposure during the first, second, and 
third trimester of pregnancy compared to unexposed will be studied as applicable to the 
following pregnancy outcomes: prete rm delivery, small for gestational age, and small for age 
postnatal growth at one year of age.
A variable for prior COVID- 19 infection will be used in the propensity score generation for 
the adjusted analyses, and, if numbers permit, a stratified analysis for prior COVID -19 
infection will be conducted as well.
12.4.2. Individual Dose Effects
We will address the potentially  differential effects of the 1st, 2nd, 3rd, and booster doses of the 
Pfizer -BioNTech COVID- 19 vaccine during the relevant pregnancy  window . Each dose will 
be considered a separate exposure, and a marginal structural model (Robins et al., 2000; 
Hernán et al., 2001 )with independent effects for the exposures will be evaluated for each 
pregnancy outcome. 
Binary  Outcomes: For an exposure window of interest, let  , , , and be indicators 
for exposure to the 1st, 2nd,  3rd, and booster dose s, respectivel y, during the window; i.e. =
1if the thdose occurs during the window and = 0otherwise, for  =1, 2, 3 and 4 . The 
sequence (, , , )describes the pattern of exposures during the window. Let 
,,,be the potential outcome that would occur if a woman was subject to the 
exposures  =  , =  , =  and =  , where each of , , and are 0or 
1. The linear logistic MSM with additive effects for each vaccine dose assumes the fo rm
logit  ,,,= 1 =  +  +  +  +  .
In this model, is the log OR representing the causal effect of exposure to the thdose. The 
causal effects are estimated from the observed data using an I PTW estimator.
The weights for the IPTW estimator will be constructed from regression models for each of 
the exposure doses  , , , and , adjusted for the selected confounders . Let ()be 
the probability  of receiving the 1stdose during the exposure window conditional on among 
subjects that received doses prior to the exposure window . Let(,  )be the probability  
of receiving the 2nddose during the exposure window conditional on among those subjects 
with =  and who received doses prior to the start of the window. Likewise, let 
(,  , )be the probability  of receiving the 3rddose during the exposure window 
conditional on among those subjects with =  and =  and who received doses 
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Page 35prior to the start of the window. Finall y, let (,  , , )be the probability  of receiving 
the 4thdose during the exposure window conditional on among those subjects with  =
, =  and =  and who received doses prior to the start of the window. The 
weight for a subject with exposures , , , and  and confounders is  = 1/ , 
where can be decomposed in terms of (), (,  ), (,  , ),and 
(,  , , )as follows:
1)= 0, = 0,  = 0, and  = 0:
= 1 −  (0)if they  have received no doses prior to the window
= 1 −  (1, 0) if they  have received one dose prior to the window
= 1 −  (2,0,0) if they  have received two doses prior to the window
= 1 −  (3,0,0,0) if they  have received three doses prior to the window
= 1if they  have received four doses prior to the window
2)= 1, = 0,  = 0, and  = 0: =  (0)(1 −  (0,1))
3)= 0, = 1,  = 0, and  = 0: =  (1,0)(1 −  (1,0, 1))
4)= 0, = 0,  = 1, and  = 0: =  (2,0,0)(1 −  (2,0,0, 1))
5)= 0, = 0,  = 0, and  = 1: =  (3,0,0,0)
6)= 1, = 1,  = 0, and  = 0: =  (0) (0,1)(1 −  (0,1, 1))
7)= 0, = 1,  = 1, and  = 0: =  (1,0)(1,0,1 )(1 −  (1,0,1,1))
8)= 0, = 1,  = 0, and  = 1: =  (1,0)(1 −  (1,0,1 ))(1,0,1,0))
9)= 0, = 0,  = 1, and  = 1: =  (2,0,0 )(2,0,0,1)
10)= 1, = 1,  = 1, and  = 0: =  (0)(0, 1)(0,1,1 )(1 −
(0,1,1,1))
11)= 1, = 1,  = 0, and  = 1: =  (0)(0, 1)(1 −
(0,1,1 ))(0,1,1,0)
12)= 0, = 1,  = 1, and  = 1: =  (1,0)(1,0,1 )(1,0,1,1)
13)= 1, = 1,  = 1, and  = 1: =  (0) (0,1) (0,1, 1)  (0,1,1,1)
Models for the terms will be estimated using the twang package in R as described in the 
primary  anal ysis. Each model will be fit using the subset of data indicated by the arguments 
, , and ; for example, the model for (0, 1, 1) will be fit using the selected 
confounders in as predictors among subjects who received no doses prior to the window 
( = 0) and the 1stand 2nddose during the window ( = 1and = 1). The weights will 
be stabilized and trimmed (Austin and Stuart, 2015 ).
Spontaneous Abortion and Preterm Delivery : For the survival outcomes, a proportional 
hazards marginal structural model (MSM) with time- dependent covariates will be used to 
estimate the causal hazard ratio for each of the exposure doses. Similar to the primary  
analyses, let (), (), (), and  ()be indicators for exposure during the relevant 
exposure window to the 1st, 2nd, 3rdandbooster doses of the Pfizer -BioNTech COVID -19 
vaccine by time , and let ,,,denote the potential time to SAB had a subject followed 
the exposure functions , ,, and  . The marginal structural model is
,,,()=  ()exp(()+  ()+  ()+  ())
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Page 36where ,,,()is the hazard of ,,,at time , is the baseline hazard function 
representing the risk for a subject who never receives either dose during the window, and 
exp()is the causal relative risks for the effect of exposure to the thdose duri ng the 
window.
As in the primary  anal yses of the survival outcomes, the MSM can be estimated by  either 
multivariable regression or IPTW depending on whether prior infection is included as a time -
dependent confounder.
The multivariable regression model will be fit as in the primary  analy ses except that it will 
include effects for the time-dependent exposures (), (), (), and  (), which 
indicate exposure b y time to the 1st, 2nd, 3rd, and booster dose s during the exposure window, 
respectivel y.
The I PTW method is based on PS models for the time to the 1st, 2nd, 3rdandbooster dose s. 
Similar to the primary  analy sis of the survival outcomes, proportional hazards models will be 
fit for the time to each of the four doses during the exposure window, adjusting for the 
selected confounders . The models y ield estimates of the conditional survival function (|)
and density  function (|) given the confounders  =  at time , for each of the four dos es 
( = 1, 2, 3, and 4). These estimates are used to compute time- dependent PS and weights . For 
a fixed time  , consider a woman with confounders  ()who is still at risk for the outcome 
by time ; let , , ,and denote the time of exposure to the 1st, 2nd, 3rd,and booster 
doses, respectively ,if they  occur during the window . For this subject, the weight at time is 
()= 1/ ()where ()is computed as follows:
1)For a subject with = 0, = 0,  = 0, and = 0,
() =  (| ())if they  have received no doses prior to the window
() =  (| ())if they  have received one dose prior to the window
() =  (| ())if they  have received two doses prior to the window
() =  (| ())if they  have received three doses prior to the window
() = 1 if they  have received four doses prior to the window
2)For a subject with = 1, = 0, = 0, and = 0,
() = (| ()) if <  
()(|()) if ≥  
3) F or a subject with  = 0, = 1, = 0, and = 0,
() =  () if <  
()(|()) if ≥  
4)For a subject with = 0, = 0, = 1, and = 0,
() = (| ()) if <  
()(|()) if ≥  
5)For a subject with = 0, = 0, = 0, and = 1,
() = (| ()) if <  
() if ≥  
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Page 376)For a subject with = 1, = 1, = 0, and = 0,
() = (| ()) if <  
()(|() ) if≤  <  
()()(|()) if ≥  
7)For a subject with = 0, = 1, = 1, and = 0,
() =  () if <  
() () if≤  <  
()() () if ≥  
8)For a subject with = 0, = 1, = 0, and = 1,
() =  () if <  
() () if≤  <  
()() if ≥  
9)For a subject with = 0, = 0, = 1, and = 1,
() =  () if <  
() () if≤  <  
()() if ≥  
10)For a subject with = 1, = 1, = 1, and = 0,
() =
⎩⎪⎨⎪⎧(| ()) if <  
()(|() ) if≤  <  
()()(|() ) if≤  <  
()()()(|() ) if ≥  
11)For a subject with = 1, = 1, = 0, and = 1,
() =
⎩⎪⎨⎪⎧(| ()) if <  
()(|() ) if≤  <  
()()(|() ) if≤  <  
()()() if ≥  
12)For a subject with = 0, = 1, = 1, and = 1,
() =
⎩⎪⎨⎪⎧ () if <  
() () if≤  <  
()() () if≤  <  
()()() if ≥  
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Page 3813)For a subject with = 1, = 1, = 1, and = 1,
()
=
⎩⎪⎪⎨⎪⎪⎧ () if <  
()(|() ) if≤  <  
()()(|() ) if≤  <  
()()()(|() ) if≤  <  
()()()() if ≥  
The PS model for the 1stdose will be fit using data from subjects who did not receive an y 
doses prior to the exposure window. For the 2nddose, the model will be fit using data from
subjects who received at one dose prior to or during the window . Similarl y, for the 3rdand
booster dose s, the model s will be fit using data from subjects who received all previous doses 
prior to or during the window. Weight stabilization and trimming wil l be administered as in 
the primary  analy ses.
Confidence intervals for either the multiple regression or IPTW method will be computed as 
in the primary  anal yses.
12.4.3. Evaluation for a Pattern of Major Congenital Malformations
As most known human teratogens ar e associated with specific clusters of major congenital 
malformations rather than an overall increase in the risk of all specific major congenital 
malformations, a qualitative review will be conducted (Alwan and Chambers, 2015 ). The 
following steps will be taken to evaluate any pattern of major congenital malformations :
A review of major congenital malformations will be made by category , including multiple 
malformation sy ndromes, categories of major congenital malformations, such as cardiac 
malformations, limb reduction anomalies, etc. A review of specific major congenital 
malformations will be conducted taking into consideration timing and biological plausibility. 
In addition, specific defects that are plausibly related to se cond or third trimester exposure 
will also be evaluated .
12.4.4. Lost to Follow -Up
Pregnancies enrolled in the cohort study for which outcome information is unobtainable 
within 1 year after the estimated date of delivery are considered lost to follow -up. It is 
possible that outcomes among pregnancies lost to -follow -up could differ from those with 
documented outcomes. Because of differences in follow-up and reporting patterns, it is 
currently not possible to assess with any certainty what impact with regard to poten tial 
biases the lost to follow -up may have on any analysis of the cohort study. Should lost to 
follow -up rates exceed 10%, in an attempt to address this potential source of bias ,baseline 
demographic characteristics including maternal age, socioeconomic st atus, race and ethnicit y 
will be compared between those lost -to-follow -up in each cohort vs. those who are retained.
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Page 39However, the OTIS Research Center prior experience has been that the lost to follow -up rate 
is extremely low, typically 5%.
12.5. Sensitivity Ana lyses
The following sensitivity analyses will be performed for the outcome of major congenital 
malformations.
A sensitivity analysis will be performed for the outcome of major congenital 
malformations among all pregnancies excluding those that are lost -to-follow -up. The 
analysis population will be those with exposure to the Pfizer -BioNTech COVID -19 
vaccine at any time from one month prior to the first day of LMP to the end of the 
first trimester excluding those that are lost- to-follow -up. The analysis popul ation for 
the comparison cohort will be all pregnancies excluding those that are lost -to-follow -
up. The purpose of this analysis is to account for major congenital malformations that 
may occur in pregnancies that are terminated or spontaneously lost and ar e therefore 
excluded from the primary analysis of major congenital malformations among live 
births.
A second sensitivity analysis will be performed for the outcome of major congenital
malformations stratified on any abnormal finding (yes/no) among those wi th prenatal 
testing prior to enrollment.
In a third sensitivity analysis, both the exposure and comparator cohorts will be 
restricted to women who enrolled in the study during their first trimester.
A fourth sensitivity analysis will be conducted to expand the comparator cohort to 
include women who received any dose of the Pfizer -BioNTech COVID -19 vaccine 
only in their second or third trimester.
Analys is using graphical presentation based on gestational timing of exposure to the 
Pfizer- BioNTech COVID -19 vaccine will also be performed.
An additional sensitivity analysis will be performed for the outcome of preterm delivery 
stratified on elective cesarian section or labor induction leading to delivery prior to 37 
weeks’ gestation vs. delivery prior to 37 weeks’ gestation following spontaneous labor.
12.6. Interim Analyses
Descriptive analyses willbe presented in annual interim reports, but no formal interim 
statistical analysis is planned. The rationale for this is that given sample size limitations, an 
interim analysis will likely be statistically underpowered to provide informative results. Each 
report will be a composite of the cumulative data to date and will supersede any previous 
reports. At each interim Scientific Advisory Board review, consideration will be given to any 
findings that might indicate that a formal interim analysis should be performed. The final 
analysis will be conducted when the cohort study has been completed.
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Page 4012.7. Analysis Software
All summaries and statistical analyses will be performed using the current version of open-
source statistical programming language R and StatXact.
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4. Austin PC and Stuart E (2015). Moving towards best practice when using inverse 
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to prevent coronavirus disease 2019 (COVID- 19) for use in individuals 12 y ears of age 
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Page 4337. Xu R, L uo Y, Gl ynn R, Joh nson D, Jones KL , and Chambers C. (2014). Time -
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Page 4414.LIST OF TABLES
Table 1. Sample Size and Power for a Specified Effect Size ................................ .12
Table 2. Variables Related to Defining the Exposure, Comparator, 
Outcomes, Exclusions, and Date/Time................................ ..................... 17
Table 3. Demographic and Clinical Variables ................................ ........................ 23
Table 4. Denominators for Outcomes by  Exposure/Comparator Cohort ............... 28
15.LIST OF FIGURES
None.
ANNEX 1. LIST OF STAND- ALONE DOCUMENTS
None.
ANNEX 2. ADDITIONAL INFORMATION
Table A -1. List of known human teratogens
Exposure Notes
Angiotensin- converting enzy me 
inhibitors/ Angiotensin II receptor 
blockersExposure in the 2ndor 3rdtrimester
Acitretin Any exposure within 2 years of LMP.
Alcohol Use, Heav y Must average 14 or more standard drinks over 
four or more weeks post -conception
Aminopterin Exposure occurring on or after LMP
Antiseizure / Anticonvulsant 
MedicationsExposure occurring on or after LMP
Antineoplastics, Other Exposure occurring on or after LMP
Cocaine Exposure occurring on or after LMP
Cytomegalovirus (CMV) Primary  infection occurring on or after LMP
Type I and T ype II Diabetes Any diagnosis
Etretinate Any exposure within 10 y earsof LMP.
Fever, High 102 degrees or higher for 24 hours or longer on 
orafter LMP
Fluconazole, Sy stemic >7 day s total (consecutive or non -consecutive) on 
or after LMP
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Page 45Table A -1. List of known human teratogens
Exposure Notes
Isotretinoin Exposure occurring on or after LMP
Lenalidomide Exposure occurring on or after LMP
Lithium Exposure occurring on or after LMP
Methimazole Exposure occurring on or after LMP
Methotrexate Exposure occurring on or after LMP
Propy lthiouracil (PTU) Exposure occurring on or after LMP
Radiation, High Dose >5 rads to the uterus on or after LMP
Rubella Exposure occurring on or after LMP
Thalido mide Exposure occurring on or after LMP
Toxoplasmosis Primary  infection occurring on or after LMP
Varicella Primary  infection occurring on or after LMP
Vitamin A, High Dose >50,000 IU per day  on or after LMP
Warfarin (Coumadin, Jantoven) 
derivatives Exposure occurring on or after LMP
Zika, Confirmed Positive test result
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