Reviewer Guidance

Evaluating the Risks of Drug 

Exposure in Human 

Pregnancies 

U.S. Department of Health and Human Services 

Food and Drug Administration 

Center for Drug Evaluation and Research (CDER) 

Center for Biologics Evaluation and Research (CBER) 

April 2005 

Clinical/Medical 

J:\!GUIDANC\6777fnlcln7.doc 

4/14/2005 
Reviewer Guidance 

Evaluating the Risks of Drug 

Exposure in Human 

Pregnancies 

Additional copies are available from: 

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Division of Drug Information, HFD-240 

Center for Drug Evaluation and Research 

Food and Drug Administration 

5600 Fishers Lane 

Rockville, MD 20857 

(Tel) 301-827-4573 

http://www.fda.gov/cder/guidance/index.htm

or 

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Manufacturers Assistance, HFM-40 

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1401 Rockville Pike, Rockville, MD 20852-1448 

(Tel) 800-835-4709 or 301-827-1800 

http://www.fda.gov/cber/guidelines.htm 

U.S. Department of Health and Human Services 

Food and Drug Administration 

Center for Drug Evaluation and Research (CDER) 

Center for Biologics Evaluation and Research (CBER) 

April 2005 

Clinical/Medical 
TABLE OF CONTENTS 

I. INTRODUCTION............................................................................................................. 1

II. BACKGROUND ............................................................................................................... 2

III. CRITICAL FACTORS IN EVALUATING THE EFFECTS OF DRUG 

EXPOSURE IN HUMAN PREGNANCIES................................................................... 4

A. Background Prevalence of Adverse Pregnancy Outcomes ........................................................4

B. Combined vs. Individual Rates of Birth Defects .........................................................................6

C. Major vs. Minor Birth Defects......................................................................................................7

D. Timing of Exposure........................................................................................................................8

E. Intensity of Exposure...................................................................................................................10

F. Variability of Response................................................................................................................11

G. Class Effects..................................................................................................................................12

IV. SOURCES OF HUMAN DATA ON GESTATIONAL DRUG EXPOSURES ......... 12

A. Case Reports.................................................................................................................................13

B. Epidemiology Studies...................................................................................................................13

1. Prospective Studies ........................................................................................................................14

a. Cohort studies .........................................................................................................................14

b. Pregnancy exposure registries ................................................................................................15

2. Retrospective Studies .....................................................................................................................16

a. Birth defect registries..............................................................................................................16

b. Case control studies................................................................................................................16

V. RESOURCES FOR MORE INFORMATION ............................................................ 17

VI. OVERALL ASSESSMENT OF POSTMARKETING HUMAN DATA................... 18

VII. LABELING ..................................................................................................................... 19

REFERENCES............................................................................................................................ 20 

ATTACHMENTS 

A. Critical Periods in Human Development...................................................................................24

B. Considerations when Evaluating Case Reports of the Effects of Drug Exposure During 

Pregnancy .....................................................................................................................................26

C. Considerations when Evaluating Epidemiology Studies on the Effects of Drug Exposure 

During Pregnancy ........................................................................................................................27
Contains Nonbinding Recommendations 

Reviewer Guidance1

Evaluating the Risks of Drug Exposure 

in Human Pregnancies 

This guidance represents the Food and Drug Administration’s (FDA’s) current thinking on this topic. It 

does not create or confer any rights for or on any person and does not operate to bind FDA or the public. 

You can use an alternative approach if the approach satisfies the requirements of the applicable statutes 

and regulations. If you want to discuss an alternative approach, contact the FDA staff responsible for 

implementing this guidance. If you cannot identify the appropriate FDA staff, call the appropriate 

number listed on the title page of this guidance. 

I. INTRODUCTION 

This guidance is intended to help FDA staff evaluate human fetal outcome data generated after 

medical product exposures during pregnancy.2

 The goal of such evaluations is to assist in the 

development of product labeling that is useful to medical care providers when they care for 

patients who are pregnant or planning pregnancy. The review of human pregnancy drug 

exposure data and assessment of fetal risk (or lack of risk) requires consideration of human 

embryology and teratology, pharmacology, obstetrics, and epidemiology. Consequently, FDA 

staff also are encouraged to consult with experts in these fields, as appropriate. 

This guidance does not address the assessment of experimental animal reproductive toxicology 

data. A separate guidance is under development for FDA pharmacology/toxicology reviewers 

that describes a process using nonclinical data to estimate human developmental and 

reproductive risks from drug exposure when human data are unavailable.3

 

1

 This guidance has been prepared by the Pregnancy Outcomes Working Group of the FDA Pregnancy Labeling 

Taskforce in the Center for Drug Evaluation and Research (CDER) and the Center for Biologics Evaluation and

Research (CBER) at the Food and Drug Administration. 

2

 Throughout this document, the terms medical product and drug include drug and biological products including

vaccines. 

1

3

 In November 2001, the FDA issued a draft reviewer guidance on Integration of Study Results to Assess Concerns

about Human Reproductive and Developmental Toxicities. When finalized, it will represent the Agency’s thinking

on this issue. (http://www.fda.gov/cder/guidance/index.htm) 
Contains Nonbinding Recommendations 

FDA’s guidance documents, including this guidance, do not establish legally enforceable 

responsibilities. Instead, guidances describe the Agency’s current thinking on a topic and should 

be viewed only as recommendations, unless specific regulatory or statutory requirements are 

cited. The use of the word should in Agency guidances means that something is suggested or 

recommended, but not required. 

II. BACKGROUND 

The term teratogen is used to denote the result of a hazard assessment on a particular agent (for 

purposes of this guidance, a drug). The use of the term indicates that the drug has the capacity 

under certain exposure conditions to produce abnormal development in an embryo or fetus. 

However, hazard assessment must be put into context. Whether a drug causes abnormal 

development or not depends not only on the physical and chemical nature of the drug but also on 

the dose, duration, frequency, route of exposure, and gestational timing involved. 

Other factors that may determine whether a particular exposure is likely to be teratogenic in a 

particular instance include other concurrent exposures and the biological susceptibility of the 

mother and the embryo or fetus. Throughout this guidance, the term teratogen is used to 

designate products with teratogenic potential at clinical doses used in humans. Classifying a 

drug as a teratogen only indicates that it may have the potential for producing developmental 

toxicity given the appropriate conditions. For example, a single 50-mg dose of thalidomide 

administered on the 26th day after conception has a significant risk of producing a major 

structural malformation of the embryo. However, that same dose of thalidomide taken in the 

10th week after conception does not produce structural malformations, and a 1-mg dose at any 

time during pregnancy has no observable effect on the developing embryo or fetus (Brent 2001). 

About 4 percent (1/28) of babies are born each year with a major birth defect or congenital 

malformation (March of Dimes 2001). The March of Dimes defines a major birth defect as an 

abnormality of structure, function, or metabolism that either is fatal or that is present at birth and 

results in physical or mental disability (March of Dimes 2001). For the majority of major birth 

defects (about 65 percent), the etiology is unknown (Schardein 2000). Chemically induced birth 

defects, including those associated with drug exposure, probably account for less than 1 percent 

of all birth defects; few drugs are proven human teratogens at clinical doses (Koren 1998). Of 

the thousands of drugs available, only about 20 drugs or groups of drugs (most being 

anticonvulsants, antineoplastics, or retinoids) are recognized as having an increased risk of 

developmental abnormalities when used clinically in humans (Schardein 2000). However, since 

few drugs have been systematically studied to identify their full range of possible teratogenic 

risks, we cannot assume that current knowledge is complete. The identification of a drug’s 

teratogenic potential is important because drug-induced adverse fetal effects are potentially 

preventable.

2
Contains Nonbinding Recommendations 

There appears to be a general perception that the use of any drug at any time during pregnancy 

can harm the developing embryo or fetus. In one study, pregnant women exposed to certain 

nonteratogenic drugs believed that the risk for major birth defects was 24 percent, which is 

similar to the known risk from exposure to thalidomide during the gestational time of most 

sensitivity (Koren 1989). Another study (done in Canada) reported that even health 

professionals who were shown drug labeling with “reassuring” text (i.e., labeling that explicitly 

stated that the drug itself does not cause fetal malformations when used in pregnancy) still rated 

those drugs as having some risk for causing birth defects (Pole 2000). This exaggerated fear 

could lead to termination of a wanted pregnancy or to unnecessary withholding of needed drug 

therapy during pregnancy. 

Although knowledge of teratogenic potential is a critical part of a drug’s benefit/risk profile, 

pregnant women are rarely included in clinical trials (Mastroanni 1994). There may be 

inadvertent pregnancy exposures during clinical trials of new products, but available data are 

usually insufficient to permit an adequately powered statistical analysis. Consequently, when a 

drug is first marketed there are usually no human data on the effects of in utero drug exposure. 

The only data on fetal effects initially available in the product labeling usually comes from

animal reproductive toxicology studies. 

Despite the lack of information on the safety of drug use during pregnancy, most pregnant 

woman likely will be exposed to drugs. Fetal exposure can occur before a woman knows she is 

pregnant. Some women enter pregnancy with medical conditions that require continuing drug 

therapy. New medical problems may develop during, or old ones may be exacerbated by, 

pregnancy. 

Because little is known before marketing about a drug’s teratogenic potential, postmarketing 

surveillance of drug use in pregnancy is critical to the detection of drug-induced fetal effects. 

With current postmarketing surveillance methods, this process can take considerable time. For 

example, with thalidomide, it took almost 4 years before the link between thalidomide use during 

pregnancy and phocomelia was recognized (Lenz 1961, McBride 1961). The recognition of the 

more subtle pattern of malformations associated with warfarin use during pregnancy took more 

than 20 years (Pettifor 1975). Some drugs may induce teratogenic effects that are not clinically 

evident until many years after birth, such as the reproductive tract abnormalities associated with 

DES exposures in utero (Herbst 1975). 

It is important that the FDA and sponsors routinely review all available data on drug exposure 

during pregnancy and work together to provide up-to-date product labeling that reflects what is 

known and not known about human fetal risk or lack of risk. 

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Contains Nonbinding Recommendations 

III. CRITICAL FACTORS IN EVALUATING THE EFFECTS OF DRUG 

EXPOSURE IN HUMAN PREGNANCIES 

The following is a list of factors to consider when presented with human pregnancy data and 

faced with making a determination whether and how the data should be included in the product 

labeling. A discussion of each factor follows. 

• Background prevalence of adverse pregnancy outcomes 

• Combined vs. individual rates of birth defects 

• Major vs. minor birth defects 

• Timing of exposure 

• Intensity of exposure 

• Variability of response 

• Class effects

A. Background Prevalence of Adverse Pregnancy Outcomes 

Every pregnancy has a risk of an abnormal outcome regardless of drug exposure. Reproductive 

toxicologists generally consider the four major manifestations of abnormal fetal development to 

be growth alteration, functional deficit, structural malformation, and death (Schardein 2000). 

The purpose of collecting and evaluating data on drug exposure during pregnancy is to address 

whether a particular drug exposure increases the risk of abnormal fetal development above the 

background rate. 

Clinical classifications of pregnancy outcomes include live births, elective terminations, and fetal 

losses, i.e., spontaneous abortions (loss prior to 20 weeks post-conception), and fetal 

deaths/stillbirths (loss beyond 20 weeks post-conception) (Ventura 2000). Based on national 

data for 1996 (the most recent year for which data are available) only 62 percent of clinically 

recognized pregnancies result in a live birth; 22 percent end in elective termination and 16 

percent result in spontaneous abortions (1 of 7 known pregnancies) or fetal death/stillbirth (1 of 

200 known pregnancies) (Ventura 2000, March of Dimes 2001). Among live births, preterm

birth (before the 35th week after conception) and low birth weight (<2500 grams) are also 

considered adverse pregnancy outcomes occurring in 1 of 8 and 1 of 12 live births, respectively 

(March of Dimes 2001). 

Although the March of Dimes reports an overall background birth defect prevalence of 4 percent 

of births, this percentage can change depending upon the definition of birth defect (e.g., inclusion 

of abnormalities of cosmetic importance), the specific population studied, and the time period 

beyond birth used for detection. The term birth defects, as used by the March of Dimes, refers to 

congenital anomalies identified by codes 740-759 of the Ninth Revision of the International 

Classification of Diseases (ICD-9) (Petrini 1997). The rate of some birth defects will be 

influenced by whether prenatally diagnosed defects and/or elective terminations are included, 

and whether prenatal defects are confirmed postnatally. For example, a large percentage of 

pregnancies with anencephaly are terminated and will not be captured in birth statistics other 

4
Contains Nonbinding Recommendations 

than as a termination. Prenatally diagnosed hydronephrosis and ventricular septal defects may 

resolve before delivery or soon afterward and will be overcounted if included only on the basis 

of prenatal diagnosis. Unfortunately, prenatally diagnosed defects may not be evaluated 

postnatally at all if the outcome is a stillbirth or elective termination. This not only precludes 

confirmation of the diagnosis, but also the ability to ascertain additional less obvious conditions. 

To assess whether the therapeutic use of a drug results in an increase in adverse fetal effects, one 

commonly compares the rate of birth defects seen in a study population to some background rate. 

However, all-inclusive background rates of all major birth defects may include infants with 

genetic syndromes and chromosomal abnormalities that may not be caused by a medication or

other toxic exposure. Therefore, at best such rates constitute very crude comparisons. 

Population estimates can vary considerably by maternal age, race, geographic region, 

socioeconomic status, and time period (e.g., the availability of diagnostic tools can change over 

time). In addition, maternal disease states (e.g., diabetes) can influence pregnancy outcomes and 

fetal development with outcome rates within a particular disease population being very different 

from rates for the general population. Therefore, when evaluating whether exposure to a drug 

during pregnancy increases the risk for any adverse pregnancy or fetal outcome, it helps to know 

the background rate of the outcome in a population as similar as possible to the study population. 

It is easier to detect an increased risk for an abnormal outcome that occurs at a relatively high 

background rate (e.g., spontaneous abortion) than it is to detect an increased risk for an abnormal 

outcome that occurs at a relatively low background rate (e.g., oral clefts). Consequently, the 

statistical power of a study to detect an increased risk of adverse fetal effects that normally occur 

at a low rate is often limited. When collecting pregnancy exposure data on a previously 

unidentified teratogen that behaves like isotretinoin in causing serious, obvious effects in about 

25 percent of exposed live-born infants, it will not take many exposed pregnancies before the 

problem is detected. However, a teratogen that behaves like valproic acid, which causes neural 

tube defects at a rate of 1 to 2 percent in exposed infants (a tenfold increase over background), 

requires a much larger number of exposed pregnancies to detect. One report of 12 normal 

infants following gestational exposure to valproic acid (Hiilesma 1980) was misleading because 

the number of exposures was not sufficient to detect an effect size of 1 to 2 percent. It took a 

retrospective case control study to demonstrate the association (Bjerkedal 1982, Robert 1982). 

When reviewing studies or case series, a reviewer should consider whether there are enough 

exposures to demonstrate an increase in risk if such a risk exists. Any studies reporting no 

increase in the background rate of birth defects in exposed pregnancies can be viewed with 

skepticism unless the power of study to detect or rule out a stated level of risk is also included 

(Ferencz 2000). 

5
Contains Nonbinding Recommendations 

B. Combined vs. Individual Rates of Birth Defects 

Human teratogens generally increase rates of specific defects or a spectrum of defects. For 

example, thalidomide causes limb, spine, and central nervous system (CNS) defects; isotretinoin 

causes ear, CNS, and cardiac defects; valproic acid causes neural tube defects; warfarin causes 

cartilage defects; and angiotensin II converting enzyme (ACE) inhibitors cause renal functional 

effects (Mitchell 2000). 

In addition to evaluating the overall rate of birth defects in the study population, it is also 

important to look at rates of individual birth defects. A population that experiences a tenfold 

increase in a specific rare birth defect (e.g., spina bifida from 0.04 percent to 0.4 percent) as a 

result of exposure to a teratogen may still have a total birth defect rate (i.e., all malformations) 

that is not measurably different from that in a reference population. 

It has been suggested that the possibility of detecting a teratogen can be increased by grouping 

individual malformations according to an understanding of their embryologic tissue of origin 

(Mitchell 2000, Scheuerle 2002). Mitchell uses the example where interference with the normal 

development of the neural crest would lead to malformations of tissues derived from neural crest 

cells which, in the earliest stages of embryogenesis, migrate to form a variety of structures 

including those of the face/ears, parts of the heart, and the neural tube. A case in point is 

isotretinoin which interferes with neural crest cell migration/development and leads to specific 

malformations of the ear, heart, and neural tube (Mitchell 2000). 

 

For general information on background population rates, refer to Table 1, which lists the leading 

categories of birth defects according to the March of Dimes, whereas Table 2 lists the range of 

reported state-level rates for some individual birth defects as reported to the National Birth 

Defects Prevention Network. 

Table 1. Leading Categories of Birth Defects

Birth Defect Estimated 

Prevalence 

Heart and circulation 

Muscles and skeleton 

Genital and urinary tract 

Nervous system and eye 

Respiratory tract 

Metabolic disorders 

1 in 115 births 

1 in 130 births 

1 in 135 births 

1 in 235 births 

1 in 900 births 

1 in 3,500 births 

Source: March of Dimes, National Perinatal Statistics 

(http://www.modimes.com)

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Contains Nonbinding Recommendations 

Table 2. Birth Defect Surveillance Data from Selected States*

Birth Defect Range in Rates per 

10,000 Live Births 

Anencephalus 

Anophthalmia/microphthalmia 

Anotia/microtia 

Atrial septal defect 

Cleft lip with and without cleft palate 

Cleft palate without cleft lip 

Endocardial cushion defect 

Esophageal ataresia/tracheosophageal fistula 

Gastroschisis 

Hydrocephalus without spina bifida 

Hypoplastic left heart syndrome 

Hypospadias and epispadias 

Microcephalus 

Obstructive genitourinary defect 

Omphalocele 

Pulmonary valve atresia/stenosis 

Pyloric stenosis 

Rectal and large intestinal atresia/senosis 

Reduction deformity: lower limbs 

Reduction deformity: upper limbs 

Spina bifida without anencephalus 

Tetralogy of Fallot 

Transposition of great vessels 

Ventricular septal defect 

0.00 – 4.92 

0.39 – 3.73 

0.19 – 6.43 

10.51 – 70.29 

4.48 – 22.98 

3.52 – 9.35 

1.11 – 6.84 

0.83 – 5.20 

0.90 – 6.59 

0.59 – 19.34 

0.51 – 3.94 

1.59 – 46.61 

0.51 – 15.65 

3.43 – 35.26 

0.45 – 3.48 

1.17 – 20.71 

0.18 – 30.70 

1.02 – 9.02 

0.74 – 5.35 

0.75 – 5.02 

1.36 – 8.08 

1.49 – 8.08 

1.02 – 6.68 

8.41 – 79.18 

*

Rates represent data contributed to the National Birth Defects Prevention Network from

30 states. Rates for most of the states were based on 5 years of data from 1995 – 1999. 

However, four states provided data for only 1 to 3 years. Not all states reported data for all 

defects. State birth defect surveillance programs vary considerably in their methodologies, 

definitions, and inclusion criteria. Because of these differences, the data cannot be 

combined to give overall rates for the United States; therefore data are presented as a range 

of rates. 

Source: National Birth Defects Prevention Network, 2002, “Birth Defects Surveillance 

Data from Selected States, 1995 – 1999,” Teratology, 66:S129-S211. 

C. Major vs. Minor Birth Defects 

Most case reports and studies of birth defects focus on major birth defects (i.e., those 

incompatible with life or requiring medical/surgical intervention). The term minor birth defect

generally refers to minor physical anomalies with less clinical importance that represent 

deviations from what is considered normal and do not have obvious medical, surgical, or 

7
Contains Nonbinding Recommendations 

cosmetic consequences. Minor birth defects are more common than major ones, occurring in 14 

to 40 percent of live births (Leippig 1987). Clearly, what constitutes a minor birth defect may be 

subjective, hence the wide range of prevalence estimates. 

Minor birth defects may have predictive value in identifying more serious associated problems. 

Estimates of the predictive value of three or more minor birth defects for an associated major 

defect range from 19.6 to 90 percent (compared to 1.3 to 2.4 percent of those with no minor birth 

defects) (Leippig 1987). Identification of a higher-than-expected frequency of infants with three 

or more minor defects, and especially a specific pattern of these defects, may be a more sensitive 

screen for possible human teratogens than evaluation of the increased risk of any major birth 

defect (Chambers 2001). Assessing minor birth defects in children who have a major birth 

defect is also important because a complete description of all abnormalities can help identify a 

pattern characteristic of the exposure and improve the ability to attribute causality. A pattern of 

minor defects may represent the mild end of a spectrum of effects with a major defect, occurring 

less frequently, at the other end of the spectrum. For example, the spectrum of effects resulting 

from in utero exposure to carbamazepine ranges from 11 percent of exposed infants with minor 

craniofacial defects and nail hypoplasia to 1 percent of exposed infants with a neural tube defect 

(Jones 1989, Hernandez-Diaz 2001). 

D. Timing of Exposure 

When interpreting data on drug exposure during pregnancy, it is important to consider the timing 

and duration of exposure and their relationship to windows of developmental sensitivity. Agents 

that produce adverse effects on the fetus typically do so during discrete sensitive periods of fetal 

development that vary depending on the particular teratogenic process and target organ. Each 

part, tissue, and organ of an embryo has a critical period during which its development may be 

disrupted (see Attachment A). For example, the most critical period for brain development is 

from 3 to 16 weeks post-conception, but its development may be disrupted after this because the 

brain is differentiating and growing rapidly (Moore 1998). 

When evaluating pregnancy outcome data, it is important to identify the frame of reference for 

the reported gestational age. Determining the gestational week of exposure based on the date of 

last menstrual period versus the date of conception can produce a 2-week time difference that 

can be critical when evaluating an association between a birth defect and drug exposure. In this 

guidance, when gestational age is mentioned, it refers to time since conception. 

During the first 2 weeks after conception the developing embryo is not susceptible to 

teratogenesis (Moore 1998). Drug exposures during this time period are not known to cause 

congenital anomalies in human embryos; however, such exposures may interfere with cleavage 

of the zygote or implantation of the blastocyst and/or cause early death and spontaneous abortion 

of the embryo (Moore 1998). 

8
Contains Nonbinding Recommendations 

In humans, the embryo is most easily disrupted during organogenesis (3 to 8 weeks postconception) when the tissue and organs are forming. During this time, teratogenic agents may 

induce gross structural abnormalities readily seen at birth. However, although more common 

with teratogenic exposures during the main embryonic period, the production of important 

anatomic defects is not limited to organogenesis, as evidenced by the microcephaly seen with 

maternal alcohol abuse during the fetal period (Moore 1998). 

Later in gestation, the fetus rapidly grows and matures, undergoing active cell growth, 

differentiation, and migration, particularly in the CNS. Exposures during this period may cause 

physiologic defects such as minor anomalies of the external ear, growth retardation or functional 

disorders such as mental retardation. However, important abnormalities can also be produced by

late pregnancy exposures such as the fetal alcohol syndrome seen with alcohol abuse, the renal 

function effects seen with the use of ACE inhibitors, and the cartilage defects seen with the use 

of warfarin. 

Knowledge of the sensitive period for human target organ development facilitates optimal data 

interpretation. For example, if drug exposure occurred after the critical period of development 

for an organ, the exposure is an unlikely cause of the organ malformation (e.g., an infant born 

with transposition of the great vessels that are formed during the first trimester, who was exposed 

to the drug only in the third trimester). 

Evaluating the timing of exposure is also important when assessing the power of a study. For 

example, consider a drug that causes a tenfold increase in neural tube closure defects, from 0.1 

percent to 1 percent. Formation of the neural tube begins about day 18 after conception and, 

with normal development, the neural tube closes by the end of the fourth week of gestation 

(Moore 1998). A hypothetical study identifies 100,000 women exposed during the first trimester 

of pregnancy, but only 1,000 of the women were exposed during the sensitive period. The 1,000 

pregnancies with exposure during the sensitive period produce 10 cases of neural tube defects 

based on a 1 percent rate while 99 cases are seen in the other 99,000 pregnancies based on the 

background rate of 0.1 percent. The total of 109 affected children from 100,000 exposed 

pregnancies produces a 0.11 percent rate, which probably would not be appreciated as different 

from the background rate of 0.1 percent and would not identify the real increase due to the 

exposure to the drug. 

Table 3 lists the sensitive periods for exposure to some known teratogens. However, as a 

practical matter, the sensitive period for exposure to a drug, if there is one, is usually unknown. 

In situations where no clear toxicity has been identified, it is common to globally assess risk 

from first trimester exposures because that is the time of organogenesis. There are two potential 

sources of error in using this global approach. First, as seen in the previous example, sensitive 

time periods for a particular problem may make up a small portion of the first trimester. 

Therefore, if numbers allow, it is recommended that exposures during the first trimester be 

analyzed by gestational week post-conception of fetal development. Second, drug-induced fetal 

toxicities may not be limited to the first trimester or may produce abnormalities during more than 

9
Contains Nonbinding Recommendations 

one exposure window. If studies exclude second and third trimester exposures, they will not be

able to identify potentially important adverse effects that occur later in pregnancy, such as those 

seen with the ACE inhibitors. 

Table 3. Examples of Critical Timing of Exposure for Some Known Teratogens

Teratogen Critical Timing of Exposure 

Thalidomide Exposure between days 24 to 36 post-conception 

can produce limb and other defects (Moore 

1998). 

Diethylstilbestrol (DES) Exposure before the 9th week post-conception 

leads to a precancerous vaginal adenosis in 73 

percent of female offspring, but in only 7 percent 

of female offspring exposed after the 17th week 

post-conception. Clear-cell carcinoma has not 

been reported in female offspring who were 

exposed in utero after the 18th week postconception (Herbst 1975). 

ACE inhibitors Exposure in the 2nd and 3rd trimester of 

pregnancy is associated with fetal hypotension, 

renal tubular dysplasia, anuria-oligohydramnios, 

growth restriction, hypocalvaria, and death 

(Sedman 1995). 

Warfarin Exposure in the latter half of the 1st trimester (6 

to 12 weeks post-conception) produces the 

greatest susceptibility to skeletal features of fetal 

warfarin syndrome (Scialli 1995). 

E. Intensity of Exposure 

Dosing, including frequency and duration of exposure, is also an important consideration. 

Typically, a drug must cross the placenta and reach the fetus in sufficient concentration to cause 

an effect. Most nonprotein agents do cross the placenta, the exceptions being highly charged 

agents or certain very large molecules like heparin and insulin. Maternal changes during 

pregnancy in absorption, volume of distribution, metabolism, plasma protein binding, and 

excretion also will affect the extent to which the fetus is exposed. These parameters are dynamic 

over the course of pregnancy. For example, some products may be more readily transported 

across the placenta during late gestation than during early gestation because of an increased 

unbound fraction in maternal circulation, increased utero-placental blood flow, increased 

placental surface area, or changes in fetal circulation. Agents that undergo relatively little 

metabolism in the fetus, but are excreted into the amniotic fluid by the well-developed fetal 

kidney in the third trimester, may have greater exposure as the fetus continually swallows 

amniotic fluid. 

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Contains Nonbinding Recommendations 

All teratogens have a threshold below which adverse effects do not occur. Conversely, almost 

all exposures can be toxic to the fetus if the dose is high enough, even if only indirectly through 

maternal toxicity (e.g., low birth weight or mortality because the mother is too sick from the 

medication to eat). 

Products that interfere with fetal development may produce manifestations along a continuum of 

response that may be closely connected with a dose-response relationship. A dose-response 

curve is usually seen in animal studies, but is rarely seen in humans because of the relatively 

narrow range of standardized clinical doses. An exception is the dose-response effect in humans 

that can be seen with alcohol. Alcohol at low doses throughout pregnancy is associated with 

slightly decreased birth weight. At high doses, it has effects on fetal neurologic development, 

and at progressively higher doses, it is associated with microcephaly and other visible anatomic 

effects (Ernhart 1987). 

F. Variability of Response 

People differ in their responses to specific medications, which may at least partially be due to 

genotypically determined differences in metabolism or receptors. Just as therapeutic or adverse 

effects related to a given drug do not occur in all exposed individuals, exposures during a 

sensitive time period known to increase the incidence of adverse pregnancy outcomes may do so 

only in a fraction of those infants exposed. For example, more than half of infants with similar 

in utero exposure to phenytoin are unaffected, about one-third show some congenital anomalies, 

and only 5 to 10 percent develop fetal hydantoin syndrome (Moore 1998). 

Although the effects of known teratogens are generally predictable from a population 

perspective, the nature and extent of effects are not necessarily possible to predict in individual 

patients under similar conditions. The teratogenicity of an exposure can be influenced by both 

the maternal and fetal genotypes, which may result in differences in cell sensitivity, placental 

transport, metabolism, receptor binding, and distribution (Polifka 1999). Even at the same dose 

in the same gestational window, there can be a range of possible outcomes. Because of this 

variability, assessment of a drug’s potential teratogenesis ought to consider the full range of birth 

defects. 

It is important to remember that the concept of variability extends not only to toxic responses, 

but also to baseline attributes of populations. Birth weight, for example, varies by race and sex. 

Normative growth curves developed in Caucasian populations that are used to evaluate AfricanAmerican or Asian-American babies may result in over-diagnosis of growth impairment. 

Genetic differences in metabolism of a drug by the mother, the placenta, and the fetus may 

contribute to variation in how much of a drug’s metabolites reach fetal tissue and thereby lead to 

variable rates and types of toxicity manifested. 

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Contains Nonbinding Recommendations 

 

G. Class Effects 

Understanding the structure/activity relationships and pharmacological mode of action of a class 

of therapeutic agents in some circumstances can provide a prediction of the possible safety and 

efficacy of a new agent. However, such knowledge is generally not predictive of human

teratogenesis (Mitchell 2000). For example, thalidomide and glutethimide are closely related by 

chemical structure, but there is no evidence that glutethimide is teratogenic (Heinonen 1977). 

While the introduction of a new product from a class of drugs with known human teratogenicity 

will solicit heightened scrutiny, it cannot be assumed that the product will also be teratogenic. 

Similar findings in the animal studies for the new product compared to the class would be cause 

for more concern, whereas clean animal data would lessen the concern.

IV. SOURCES OF HUMAN DATA ON GESTATIONAL DRUG EXPOSURES 

Information on human gestational drug exposures will emerge during the postmarketing phase 

for virtually all drug products. Human pregnancy outcome data will be sent to the Agency either 

directly by voluntary reporters or via the sponsors as required by federal regulations.4

 The data 

will come from a variety of sources. For the most part, data will not be derived from controlled 

clinical trials, but from observational studies. 

No single methodology can delineate the complete spectrum of adverse outcomes associated 

with prenatal exposure to a drug. Therefore, it is important to consider information from all 

available postmarketing surveillance sources to optimize detection and characterization of the 

reproductive effects of prenatal drug exposure. 

4

 21 CFR 310.305, 314.80, 314.98, 600.80, and 600.81 require sponsors to report adverse drug experiences from all 

sources (e.g., spontaneous reports, literature, studies). All congenital anomalies are considered serious (§ 314.80(a) 

and § 600.80(a)) and must be reported to the Agency within 15 days if unexpected (§ 314.80(c)(1)(i) and 

§ 600.80(c)(1)(i)). 

The ICH guidance for industry E2C Clinical Safety Data Management: Periodic Safety Update Reports for 

Marketed Drugs provides recommendations on what to include in a periodic report. It specifically lists “positive or 

negative experiences during pregnancy or lactation” as one safety issue to be explicitly addressed in the Overall 

Safety Evaluation section of the Periodic Safety Update Report (PSUR). On March 14, 2003, the FDA published a 

proposed rule that would incorporate these requirements into the FDA’s postmarketing safety reporting regulations 

(68 FR 12406). 

12

21 CFR 314.81(b)(2)(vii), 314.98(c), and 601.70 require a sponsor to submit in an annual report the status of certain

types of postmarketing studies, including clinical safety studies, whether the FDA required the study or the applicant 

committed to it in writing. This requirement would include any epidemiologic study directed to the safety of drug

use during pregnancy (e.g., pregnancy exposure registries) to which the applicant committed in writing. 
Contains Nonbinding Recommendations 

Brief descriptions of the most common types of data and study designs follow. More in-depth 

information on the strengths and weaknesses of each can be found in pharmacoepidemiology 

texts elsewhere (Hartzema 1998, Strom 2000). 

A. Case Reports 

Case reports describe one or a series of clinical observations on drug exposure during pregnancy 

and subsequent infant effects. Case reports are the most common source of reported congenital 

anomalies, but can also be the most difficult to interpret. It is true that most pregnancy 

exposures that produce an increase in developmental risk in humans were first suggested by case 

reports (Schardein 2000). However, case reports cannot distinguish coincidence from causation 

and cannot be used to assess teratogenic risk. A series of case reports associating an unusual 

outcome with a drug exposure might well raise suspicions, as in the case of thalidomide, but 

follow-up evaluations are always necessary to assess risk. Unlike the case of thalidomide, most 

case reports that call attention to a putative association are not confirmed by follow-up 

evaluation. Case reports were the source for allegations regarding teratogenicity with Bendectin, 

but those allegations were later disproved through epidemiologic studies (Goldberg 1986). 

Conversely, case reporting of a small number of normal outcomes can delay the identification of 

an association, as was the case with valproic acid and spina bifida, where a published report of 

12 normal pregnancies was too small to detect the now known 1 percent rate of affected children 

(Scialli 1992). 

It is critical to be cautious and objective when evaluating isolated case reports because adverse 

outcomes tend to be disproportionately reported. The birth of an infant with a birth defect can be 

devastating. In an effort to understand what went wrong, health care providers and their patients 

may consider drug and other exposures during pregnancy. In contrast when a normal infant is 

born, there is no incentive to recall, much less report to the FDA or in the literature, any drug 

exposures during pregnancy. 

Although an individual case report, by itself, can never prove causality, a series of similar reports 

of a distinct abnormality or group of abnormalities can establish a strong association or signal the 

need for further research. Most signals based on case reports will need to be further investigated 

using other pharmacoepidemiologic studies. Attachment B is a checklist that may be useful 

when evaluating case reports. 

B. Epidemiology Studies 

13

Formal epidemiology studies provide the best means of evaluating whether a gestational 

exposure adversely affects the developing infant. Epidemiology studies can identify associations 

between a given drug exposure and abnormalities in the newborn, and they can quantify the 

strength of such associations. Also, although it is impossible to demonstrate absolute safety, 

epidemiology studies can provide some measure of reassurance if risks are not found to be 

elevated, and the level of reassurance, like evidence of risk, can be quantified. The degree of 

reassurance is a function of the sample size (power) of the study. A study may report a lack of 
Contains Nonbinding Recommendations 

 

association between a drug and birth defects simply because the study was insufficiently 

powered due to a small sample size to detect anything other than a very large difference. Thus, 

results from any pharmacoepidemiology study of birth defects must take into account what level 

of risk the study was capable of detecting. 

In addition to a study’s power, possible confounding by maternal indication is an important 

consideration. For example, birth defects are known to occur with increased frequency in infants 

born to women with certain medical conditions (e.g., diabetes), independent of the product used 

to treat the disease. With other diseases, it may not be known whether it is the disease, the drug, 

or an interaction between the severity of disease and the drug exposure that causes an observed 

increased risk of birth defects. For example, after years of speculation, it was only recently that a 

study suggested that the increased risk for embryopathy seen in the offspring of women with 

epilepsy is associated with gestational exposure to anticonvulsants rather than with epilepsy itself 

(Holmes 2001). 

Other maternal attributes such as age, race, weight, parity, geographic location, and 

socioeconomic status can cause confounding as well. For example, children born to young 

mothers have a higher risk of gastroschisis (Nichols 1997), and Hispanics have a higher risk of 

spina bifida (Lary 1996). 

Attachment C contains a checklist that may be useful when evaluating epidemiology studies. 

1. Prospective Studies 

a. Cohort studies 

Cohort studies enroll a group of pregnant women before pregnancy outcome is known and 

collect information periodically throughout pregnancy on personal demographics, a variety of 

exposures, including drugs, and potential confounders. Their offspring are examined at birth and 

followed for a set amount of time. An example is the U.S. Collaborative Perinatal Project (CPP) 

that enrolled about 52,000 pregnant women between 1959 and 1965, collected detailed 

information on their pregnancies, and followed the children until age seven (Heinonen 1977). 

Another pregnancy cohort study, The National Children’s Study, currently under development 

by NIH,5

 plans to study 100,000 children by enrolling pregnant women and following their 

offspring through 21 years of age. The study will periodically query the pregnant women and 

then the children about certain exposures, including therapeutic drug use. 

The strength of the cohort design is the prospective, systematic collection of data, including 

exposures, confounders, and outcome information. If the population is large, it allows the study 

of multiple exposures and multiple outcomes. However, one major weakness of these studies is 

that generally small numbers of specific birth defects will be seen even in a large study 

population. This, coupled with the small number of women exposed to specific drugs within the 

14

5

 http://nationalchildrensstudy.gov. 
Contains Nonbinding Recommendations 

cohort, makes the detection of even a substantial drug-induced increase in the rate of any 

individual defect very difficult if not impossible. 

b. Pregnancy exposure registries 

Pregnancy exposure registries, a type of cohort study, prospectively enroll pregnant women 

exposed to one or more specific drugs of interest (unexposed pregnant women are sometimes 

included as well) and evaluate the associated pregnancy outcomes. Structured interviews or 

questionnaires that gather data on drug exposures and other confounders are administered 

periodically through pregnancy and often up until the infant is 1 year old. Some registries also 

include an evaluation of all live born infants by a dysmorphologist (Chambers 2001). Adverse 

pregnancy outcome rates in the exposed cohort are compared to rates in a non-exposed group 

drawn either from the study itself or from population data. 

This design is the most efficient way to collect information on exposures with newly marketed 

drugs and potentially allows for evaluation of a range of adverse outcomes including patterns or 

a spectrum of malformations and functional deficits. However, this type of study is likely to 

undercount spontaneous abortions that occur because a pregnancy registry would never be able 

to detect drug-induced fetal losses that occur before pregnancy is known. 

The length of time an infant is monitored and the source of information about the infant can 

influence the number of defects detected. One study reported that registries that limited infant 

data collection to information from the maternal health care provider on the infant’s status at 

birth were less likely to ascertain either multiple defects per case or internal and serious defects, 

particularly genitourinary defects (Honein 1999). 

The choice of an appropriate comparison group is a challenging aspect of pregnancy exposure 

registries. Comparison to the general population background rate of birth defects, although 

useful as a first screen, does not take into account the influence of relevant maternal attributes 

that may be related to the occurrence of birth defects, such as disease state, age, weight, use of 

alcohol or tobacco, or socioeconomic status. The ideal comparison group would be provided 

through concurrent enrollment of a group of pregnant women similar in all regards (including the 

disease leading to drug exposure) except for the specific drug exposure, but this is very difficult 

to implement. 

Registries are often limited by self-referral bias (where women who enroll in the registry may be 

more or less likely to have malformed infants). Losses to follow-up can also limit the 

interpretability of registry data. Losses may be related to whether the infant is normal or not, 

particularly if the mother is not the primary provider of information to the study. 

Pregnancy exposure registries tend to be too small or limited to resolve concerns about a drug 

increasing the risk of specific birth defects; however, they can potentially detect teratogens that, 

like thalidomide or isotretinoin, are so powerful that they produce defects in a relatively high 

15
Contains Nonbinding Recommendations 

 

proportion of exposed pregnancies. Thus, a cohort of only a few dozen or 100 women exposed 

to such a drug would be sufficiently large to identify major teratogens. This ability is

demonstrated with isotretinoin where 36 women with first trimester exposures were identified 

prospectively and followed through their pregnancies. Of the 28 live-born infants, five (18 

percent) were malformed (Lammer 1985). Furthermore, because pregnancy registries may have 

the capacity to conduct specific examinations of infants born to exposed and unexposed mothers, 

including up until the time the child is 1 year old, they can identify outcomes other than major 

structural malformations, such as a developmental delay. 

Postmarketing pregnancy exposure registries are being increasingly used proactively to monitor 

for major fetal effects. Sponsors may develop pregnancy exposure registries, either on their own 

initiative or when requested by the FDA as a postmarketing commitment. In 2002, the Agency 

published industry guidance on establishing pregnancy exposure registries to encourage the a 

priori development of epidemiologically sound, written, study protocols.6

 The Pharmacist’s 

Guide to Pregnancy Registry Studies provides a basic checklist for evaluating pregnancy 

exposure registries (Weiss 1999). A list of current pregnancy exposure registries enrolling 

women is available at http://www.fda.gov/womens/registries/default.htm.

2. Retrospective Studies 

a. Birth defect registries 

Birth defect registries such as the Centers for Disease Control and Prevention’s (CDC’s) 

Metropolitan Atlanta Congenital Defects Program (Edmonds 1981) and the International 

Clearinghouse for Birth Defect Monitoring Systems (International Centre for Birth Defects 

2000) monitor temporal and geographic frequencies of birth defects. The concept of these 

registries is that the introduction of a new major teratogen would lead to an unusual frequency or 

clustering of particular defects. Although no drug teratogen has ever been detected using a birth 

defect registry (Khoury 1987), the registries have been used to identify cases for use in case 

control studies (Robert 1982) and to provide population-based birth defect rates for use as a 

comparator in pregnancy exposure registries (Honein 1999). 

b. Case control studies 

Case control studies enroll infants with specific birth defects and collect data on gestational 

exposures, including drugs. The frequency of drug exposure in the cases is compared with the 

frequency of exposure to the same drug in a group of controls without the birth defects of 

interest. Information on drug exposure is usually obtained retrospectively by interviews, 

questionnaires, or review of medical records. Case control studies can be conducted on an ad 

hoc basis or as part of an ongoing case control surveillance study such as the Slone 

16

6

 See guidance for industry Establishing Pregnancy Exposure Registries. 

(http://www.fda.gov/cder/guidance/index.htm)
Contains Nonbinding Recommendations 

Epidemiology Center’s Birth Defects Study (Mitchell 1981) or the CDC’s National Birth Defects 

Prevention Study (Yoon 2001). 

Although pregnancy exposure registries are limited to screening for major teratogens on the level 

of thalidomide or isotretinoin, case control studies have the statistical power to identify

teratogens with more modest risks on the level of valproic acid. The main strength of case 

control studies is their ability to evaluate the risk of rare events, and in the setting of birth 

defects, this strength means that such studies are highly efficient in identifying the risk of 

specific birth defects. 

Recall bias is always of concern with case control studies. There are limitations to the specificity 

with which mothers can recall their drug exposures during pregnancy, particularly if a drug is 

used only occasionally for an indication that may not be easily recalled (e.g., analgesic for a 

headache). A mother of an infant born with a major birth defect may be more likely to carefully 

recall all gestational events and exposures than the mother of a normal infant (Werler 1989), and 

this phenomenon, though poorly documented, must be taken into account in the design and 

analysis of case control studies. One approach that can minimize the risk of recall bias is the use 

of infants with a wide range of other defects, as controls may help correct for this bias (Lieff

1999, Mitchell 2000). Another approach is the use of medical or pharmacy records to confirm

drug exposures. This would at least confirm that a drug was prescribed or a prescription filled; 

whether the drug was actually ingested would still be unknown. 

V. RESOURCES FOR MORE INFORMATION 

FDA staff have access to several external resources that can assist in assessing reproductive 

toxicities from drug exposures. The online Micromedex Integrated Index, which can be accessed 

via the FDA Medical Libraries’ WebLEARN intranet page, contains the REPRORISK system. 

This system contains electronic versions of four comprehensive, periodically updated, teratogen 

information databases, which are scientifically reviewed resources that critically evaluate the 

literature regarding human and animal pregnancy drug exposures. The four databases are: 

• REPROTEXT Reproductive Hazard Reference 

• REPROTOX (www.reprotox.org) 

• Shephard’s Catalog of Teratogenic Agents (Shephard 2001) 

• TERIS Teratogen Information System (Friedman 2000) 

Other reference texts to consult include: 

• Chemically Induced Birth Defects (Schardein 2000) 

• Drugs in Pregnancy and Lactation. A Reference Guide to Fetal and Neonatal Risk 

(Briggs 1998) 

• The Women, Their Offspring, and the Malformations (Heinonen 1977) 

17
Contains Nonbinding Recommendations 

Within the FDA, it is important for clinical reviewers to consult each other as well as pharmtox 

reviewers, drug safety evaluators, epidemiologists, and statisticians. In particular, the FDA’s 

Pregnancy Labeling Team (PLT) is available as a consultative resource. The PLT ensures that 

the FDA maintains access to experts in teratology, birth defects epidemiology, or obstetric 

clinical pharmacology who are approved Special Government Employees (SGEs) and available 

for consultation by request. 

VI. OVERALL ASSESSMENT OF POSTMARKETING HUMAN DATA 

No set formula exists that can prove that an association between a gestational drug exposure and 

adverse pregnancy outcome is, in fact, a cause-effect relationship. There are no known 

medications for which it can be said that all exposed pregnancies would be adversely affected 

and only a few medications for which it is known that a large proportion of pregnancies would 

be affected. If a relationship between medication use and adverse outcome exists, it is more 

typical for the relationship to represent a relatively small increase over the background risk. 

Therefore, it is probably not useful to approach the review of data with the question: Is this 

medication teratogenic? What is useful is to consider the following: 

• Does there appear to be an increased risk in exposed infants compared to the 

background rate seen in unexposed pregnancies? 

• If so, what is the apparent likelihood of increased risk of adverse outcome associated 

with the medication?

Evidence from all sources, including human data from case reports, epidemiology studies, and 

animal data, should be considered collectively to determine the strength of the relationship. To 

test the possibility that an association is causal, there are six commonly used assessments that 

may be helpful to apply to any accumulated data. These criteria for evaluating the causal nature 

of an association were introduced by Sir Austin Bradford Hill (Hill 1965) and subsequently 

modified for use in teratology as summarized by Scialli (Scialli 1992). 

• Strength of the Association — What is the statistical likelihood that the association 

did not occur by chance alone? Is the same level of association seen in several 

studies? 

• Consistency of the Association — Is the same association seen in several reports or 

studies? In different populations?

• Specificity of the Association — How often does the drug exposure occur without 

causing the effect, and how often does the effect occur separately from drug 

exposure?

• Appropriate Timing — Does the association make chronological sense? Was the 

drug taken at the critical time in development to affect the target organ?

• Dose-Response Relationship — Does the likelihood and magnitude of response 

increase with dose of the drug? Although a dose-response relationship is not often 

seen in human reports or studies because the same dose or a narrow range of doses is 

18
Contains Nonbinding Recommendations 

 

typically used, in animal studies the production of toxicity is expected to be dose 

dependent. 

• Biological Plausibility — Does the association make biological sense? Does the 

drug cross the placenta? Assessment of biologic plausibility requires consideration 

of the dose of a potentially toxic agent, its pharmacology, maternal and fetal 

metabolism, mechanism and targets of toxicity, variability of response, and windows 

of likely effect. For example, a product that is known to alter cardiac tissue 

development, but not known to affect vasculature, skeletal muscle, or bone 

development, is unlikely to have been responsible for limb reduction defects in the 

case of a mother exposed only in the third trimester. The type of defect seen and the 

timing of exposure make this implausible. 

VII. LABELING 

As part of the Periodic Safety Update Report (PSUR) sponsors are asked to specifically report on 

“positive or negative experiences during pregnancy or lactation,” evaluate new human data as 

they become available, in the context of what is already known about the reproductive effects of 

the drug, and, if clinically relevant, communicate conclusions regarding risk or lack of risk 

associated with gestational exposure in the product labeling.7

 The lack of human data must also 

be noted in the labeling (21 CFR 201.57(f)(6)(i)(b) and (c)). 

If there is an increased risk associated with the use of the drug during pregnancy, the labeling 

should describe, to the extent possible, the specific abnormality, the incidence, seriousness, 

reversibility, and correctability of the abnormality and the effect of dose, duration of exposure, or 

gestational timing of exposure on the likelihood of risk. 

The labeling must also include a description of all adequate and well-controlled studies that have 

failed to demonstrate a risk from gestational exposure to the drug (§ 201.57(f)(6)(i)(a) and (b)). 

Whenever possible, for all critically assessed, valid studies, the labeling should include 

confidence limits and power calculations to establish the statistical power of the study to identify 

or rule out a specified level of risk. The labeling should include and be routinely updated with 

data from ongoing studies, such as pregnancy exposure registries. 

The labeling generally should not include isolated case reports unless there has been a conscious, 

scientific judgment made by the sponsor and FDA reviewer that the quality of the reports and 

other factors (e.g., consistency with animal findings; information on dose, duration, and timing 

of gestational exposure; or biologic plausibility) support inclusion. 

19

7 See ICH guidance for industry E2C Clinical Safety Data Management: Periodic Safety Update Reports for 

Marketed Drugs. (http://www.fda.gov/cder/guidance/index.htm)
Contains Nonbinding Recommendations 

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20
Contains Nonbinding Recommendations 

Hiilesma, VK, AH Bardy, ML Granstrom, et al., 1980, Valproic Acid During Pregnancy, The 

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21
Contains Nonbinding Recommendations 

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22
Contains Nonbinding Recommendations 

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23
Contains Nonbinding Recommendations 

ATTACHMENT A 

Critical Periods in Human Development 

Attachment A, which appears on the following page, was taken from The Developing Human: 

Clinically Oriented Embryology (Moore, KL and TVN Persaud, 1998, sixth edition, 

Philadelphia: W.B. Saunders Company, p. 548) and reproduced with permission. For an 

accurate interpretation of the diagram, it should be printed in color. 

24
Contains Nonbinding Recommendations 

25
Contains Nonbinding Recommendations 

ATTACHMENT B 

Considerations when Evaluating Case Reports of the Effects of Drug Exposure 

During Pregnancy 

• Is there information on drug dose?

• Is there information on dates of drug therapy? 

• Is the date of conception or the LMP given?

• Does the drug cross the placenta? 

• Was the drug given at the appropriate time during gestation to cause the reported fetal 

effect or problem?

• Were any other medications given to the mother? If so, are they associated with any birth 

defects?

• What maternal attributes are included (e.g., age, race, other)? Could they be associated 

with the reported fetal effect? 

• What is known about the mother’s medical history?

• What is known about maternal and paternal family histories of birth defects?

• If the drug was given for treatment of a maternal disease, what is known about fetal 

effects associated with that maternal disease? 

• Does the reported fetal effect have any familial or genetic associations? 

• Did a physician evaluate and confirm the infant’s condition? What is the level of 

expertise of the person who made the diagnosis? 

• What types of developmental problems were seen in the animal studies? Is the reported 

human effect similar in presentation or mechanistically? 

• Are there any other similar human reports in AERS or in the literature?

• What do the REPRORISK system and other reference texts say about the drug?

• Are similar fetal effects seen with pharmacologically similar drugs? 

NOTE: If important data are missing from the case report, the initial reporter should be 

contacted. 

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ATTACHMENT C 

Considerations when Evaluating Epidemiology Studies on the Effects of Drug 

Exposure During Pregnancy 

Exposure information 

• Are dose, duration, and timing of exposure included?

• How are exposures reported and/or confirmed (e.g., patient report, health care 

professional report, medical/pharmacy records)? 

• With case control studies, what is the length of time between birth and obtaining 

information on exposures during pregnancy? 

Loss to follow-up 

• What is the proportion lost to follow-up?

Outcome ascertainment 

• What outcomes were evaluated (e.g., spontaneous abortion, still birth, congenital 

anomalies, neurodevelopmental toxicities)?

• When is outcome ascertained? 

• Who is the source of outcome information (e.g., mother, maternal health care provider, 

infant health care provider)? 

• Are reported adverse outcomes confirmed with medical records?

• Are normal live births confirmed with medical records?

• What is the length of follow-up on the infant (e.g., only at birth, up to 1 year of age)?

Additional factors and influences on pregnancy outcome (potential confounders) 

• What additional information is collected (e.g., indication, concomitant medications, 

medical and family history, previous pregnancies and outcomes, socio-demographics, 

smoking, alcohol consumption)?

Comparison group 

• What type of comparison group was used?

• Did the study have an internal comparison group?

• With case control studies, what is the impact of the comparison group on recall bias?

Representativeness 

• How representative of the U.S. general population is the population covered by the 

study?

Analysis and Interpretation 

• How was the risk of each outcome calculated? Were all exposures in the denominator 

eligible to be in the numerator? 

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28

• How does the loss to follow-up influence the study results? 

• How are the data grouped for analysis based on timing of exposure (e.g., by trimester, by 

weeks of gestation)? 

• How does the study address concerns raised by animal studies? Are there other relevant 

outcomes that the study was not able to address? 

Power 

• What level of risk is the study powered to evaluate? 

• Are confidence intervals provided?