Selection bias in Teratology Information Service pregnancy outcome studies

Belimumab use during pregnancy: a summary of birth defects and pregnancy loss from belimumab clinical trials, a pregnancy registry and postmarketing reports

OBJECTIVE

Describe available data on birth defects and pregnancy loss in women with systemic lupus erythematosus (SLE) exposed to belimumab.

METHODS

Data collected from belimumab clinical trials, the Belimumab Pregnancy Registry (BPR), and postmarketing/spontaneous reports up to 8 March 2020 were described. Belimumab exposure timing, concomitant medications and potential confounding factors were summarised descriptively.

RESULTS

Among 319 pregnancies with known outcomes (excluding elective terminations), 223 ended in live births from which birth defects were identified in 4/72 (5.6%) in belimumab-exposed pregnancies and 0/9 placebo-exposed pregnancies across 18 clinical trials, 10/46 (21.7%) belimumab-exposed pregnancies in the BPR prospective cohort (enrolled prior to pregnancy outcome) and 0/4 belimumab-exposed pregnancies in the BPR retrospective cohort (enrolled after pregnancy outcome), and 1/92 (1.1%) in belimumab-exposed pregnancies from postmarketing/spontaneous reports. There was no consistent pattern of birth defects across datasets. Out of pregnancies with known outcomes (excluding elective terminations), pregnancy loss occurred in 31.8% (35/110) of belimumab-exposed women and 43.8% (7/16) of placebo-exposed women in clinical trials; 4.2% (2/48) of women in the BPR prospective cohort and 50% (4/8) in the BPR retrospective cohort; and 31.4% (43/137) of belimumab-exposed women from postmarketing/spontaneous reports. All belimumab-exposed women in clinical trials and the BPR received concomitant medications and had confounding factors and/or missing data.

CONCLUSIONS

Observations reported here add to limited data published on pregnancy outcomes following belimumab exposure. Low numbers of exposed pregnancies, presence of confounding factors/other biases, and incomplete information preclude informed recommendations regarding risk of birth defects and pregnancy loss with belimumab use.

Estimating cumulative incidence functions in competing risks data with dependent left-truncation

Both delayed study entry (left-truncation) and competing risks are common phenomena in observational time-to-event studies. For example, in studies conducted by Teratology Information Services (TIS) on adverse drug reactions during pregnancy, the natural time scale is gestational age, but women enter the study after time origin and upon contact with the service. Competing risks are present, because an elective termination may be precluded by a spontaneous abortion. If left-truncation is entirely random, the Aalen-Johansen estimator is the canonical estimator of the cumulative incidence functions of the competing events. If the assumption of random left-truncation is in doubt, we propose a new semiparametric estimator of the cumulative incidence function. The dependence between entry time and time-to-event is modeled using a cause-specific Cox proportional hazards model and the marginal (unconditional) estimates are derived via inverse probability weighting arguments. We apply the new estimator to data about coumarin usage during pregnancy. Here, the concern is that the cause-specific hazard of experiencing an induced abortion may depend on the time when seeking advice by a TIS, which also is the time of left-truncation or study entry. While the aims of counseling by a TIS are to reduce the rate of elective terminations based on irrational overestimation of drug risks and to lead to better and safer medical treatment of maternal disease, it is conceivable that women considering an induced abortion are more likely to seek counseling. The new estimator is also evaluated in extensive simulation studies and found preferable compared to the Aalen-Johansen estimator in non-misspecified scenarios and to at least provide for a sensitivity analysis otherwise.

Ethical approval for multicenter cohort studies on drug exposure during pregnancy: A survey among members of the European Network of Teratology Information Services (ENTIS)

The European Network of Teratology Information Services (ENTIS) is in a privileged position to perform independent post-marketing surveillance of drugs in pregnancy. The aim of this survey was to describe the legal requirements and procedures involved in obtaining ethical approval for collaborative cohort studies. We sent a survey questionnaire to all 28 Teratology Information Services (TIS), of which 25 (89%) in 18 countries completed our questionnaire. For 15 TIS, specific research ethical approval was mandatory. The review process was estimated to last from 2 up to 16 weeks. Procedures for patients' information and consent were oral (12), written (5) or both (3). Five TIS had no requirement to inform patients and seek consent. Since data on drug exposure during pregnancy are scarce, ENTIS research efforts should be further encouraged, and procedures optimized so that legitimate ethical and legal requirements do not translate into deterrent administrative constraints and costs.

Angiotensin-II receptor 1 antagonist fetopathy--risk assessment, critical time period and vena cava thrombosis as a possible new feature

AIMS

Angiotensin-II receptor 1 antagonists (AT₁-antagonists) may cause severe and even lethal fetopathy in late pregnancy. However, exposure still occurs in spite of warnings in package leaflets. This study aimed to assess the risk of fetopathy, the sensitive time window, and possible new symptoms in prospective as well as retrospective cases with AT₁-antagonist treatment during the second or third trimester of pregnancy.

METHODS

Patients were enrolled by the Berlin Institute for Clinical Teratology and Drug Risk Assessment in Pregnancy between 1999 and 2011 through risk consultation. Symptoms defined as indicative of AT₁-antagonist fetopathy were: oligo-/anhydramnios, renal insufficiency, lung hypoplasia, joint contractures, skull hypoplasia and fetal/neonatal death.

RESULTS

In 5/29 (17%) prospectively enrolled cases with AT₁-antagonist exposure beyond the first trimester oligo-/anhydramnios was diagnosed. Two infants showed additional symptoms of fetopathy. The risk is more than 30% if treatment continues beyond the 20th week of pregnancy. Oligo-/anhydramnios was reversible after AT₁-antagonist withdrawal. Among 16 retrospective case reports, three infants presented with a thrombosis of the inferior vena cava in the vicinity of the renal veins. Four out of 13 live births did not survive.

CONCLUSIONS

Our survey suggests that the risk increases with duration of AT₁-antagonist treatment into late pregnancy and oligo-/anhydramnios may be reversible after AT₁-antagonist discontinuation. Thrombosis of inferior vena cava may be a new feature of AT₁-antagonist fetopathy. AT₁-antagonist medication during pregnancy constitutes a considerable risk and must be discontinued immediately. In case of indicative diagnostic findings in either the fetus or newborn, previous maternal AT₁-antagonist exposure should be considered.

Atypical antipsychotic drugs and pregnancy outcome: a prospective, cohort study

Women of childbearing age are often affected with psychotic disorders, requiring the use of antipsychotic medication during pregnancy. In the present study, we prospectively followed the pregnancies of 561 women exposed to second-generation antipsychotic agents (SGAs; study cohort) and compared these to 284 pregnant women exposed to first-generation antipsychotic agents (FGAs; comparison cohort I) and to 1122 pregnant women using drugs known as not harmful to the unborn (comparison cohort II). Subjects were enrolled through the Institute's consultation service. Major malformation rates of SGA exposed were higher compared to comparison cohort II (adjusted odds ratio, 2.17; 95% confidence interval, 1.20-3.91), possibly reflecting a detection bias concerning atrial and ventricular septal defects. Postnatal disorders occurred significantly more often in infants prenatally exposed to SGAs (15.6%) and FGAs (21.6%) compared to 4.2% of comparison cohort II. Cumulative incidences of elective terminations of pregnancy were significantly higher in both the study cohort (17%) and comparison cohort I (21%) compared to comparison cohort II (3%), whereas the rates of spontaneous abortions did not differ. The numbers of stillbirths and neonatal deaths were within the reference range. Preterm birth and low birth weight were more common in infants exposed to FGAs. To conclude, our findings did not reveal a major teratogenic risk for SGAs, making the better studied drugs of this group a treatment option during pregnancy. Because neonates exposed to SGAs or FGAs in the last gestational week are at higher risk of postnatal disorders, delivery should be planned in clinics with neonatal intensive care units.

Teratogenicity of mycophenolate confirmed in a prospective study of the European Network of Teratology Information Services

After maternal exposure to mycophenolate in pregnancy a high number of fetal losses and a specific pattern of birth defects consisting of microtia, cleft lip, and other anomalies have been reported. However, so far, prospective data on pregnancy outcome allowing quantitative risk assessment are missing. We report on 57 prospectively ascertained pregnancies after maternal therapy with mycophenolate (mycophenolate mofetil or mycophenolate sodium) identified by European Teratology Information Services (ETIS) through their risk consultation process. The outcome of these prospective pregnancies was as follows: 16 spontaneous abortions, 12 elective terminations of pregnancy (ETOP) (including two late terminations for multiple malformations consistent with mycophenolate embryopathy), and 29 liveborn infants. The probability of spontaneous abortion was about 45% (95% CI 29 to 66%) estimated using survival analysis technique. Six out of 29 live born infants had major congenital defects: Two with external auditory canal atresia (EACA) (with and without microtia), one with tracheo-esophageal atresia, one with severe hydronephrosis, one with an atrial septal defect (ASD) and one with a myelomeningocele. Thus, at least four fetuses/infants of our prospective case series had a clinical phenotype consistent with mycophenolate embryopathy. Our results confirm a high incidence of major malformations (26%) after first trimester exposure to mycophenolate. Apart from exposure to mycophenololate, the underlying maternal disease and concomitant medication may also have contributed to the other poor pregnancy outcomes such as a high rate of spontaneous abortions, prematurity (62%), and low birth weight (31%).

The role of teratology information services in screening for teratogenic exposures: challenges and opportunities

Teratology Information Services (TIS) located throughout the world have long played a key role in screening for potential new human teratogens. Using a basic prospective cohort study design, TIS recruit pregnant women from among callers to the Services who have had an exposure of interest and at the same time identify an unexposed comparison group from the same pool of callers. Women in both groups are followed to pregnancy outcome and a range of adverse outcomes including major congenital anomalies, birth size, pregnancy loss, and preterm delivery are evaluated, while controlling for potential confounding. Particularly for rare exposures or newly marketed medications, TIS may be uniquely suited to gathering this information in a timely and efficient fashion. The primary limitation of these studies is the unknown representativeness of the volunteer sample, and the typical small to moderate sample sizes. Methods to increase the proportion of exposed pregnancies that are recruited should be developed. However, small sample size TIS studies, especially when considering new or rare exposures, often fulfill the important function of providing some reassurance to women who have already had the exposure of interest by ruling out major risks for teratogenicity, that is, on the order of thalidomide. Collaborations across TIS nationally and internationally help to address the sample size challenges. A formal collaboration between the TIS cohort study model with a case-control study design is also underway and will provide complementary strengths.

Toxicological considerations for antithyroid drugs in children

INTRODUCTION

Propylthiouracil (PTU), methimazole (MMI) and carbimazole are indicated for the treatment of hyperthyroidism in adult and pediatric patients. The aim of this review is to present all the relevant information regarding the use of antithyroid drugs (ATD) in pediatric thyrotoxic cases, the pediatric toxicology of ATD and the warning which has recently been issued for PTU by the FDA.

AREAS COVERED

Epidemiology, diagnosis and treatment of pediatric thyrotoxicosis are all presented in this article. The authors also extensively discuss the details regarding the pharmacology, bioactivation, biodisposition, bioavailability and pharmacokinetic properties of the two main ATD (MMI and PTU).

EXPERT OPINION

The FDA recently reported that use of PTU is associated with a higher risk for clinically serious or fatal liver injury compared to MMI in both adult and pediatric patients. They also found that congenital malformations were reported approximately three times more often with prenatal exposure to MMI compared with PTU and especially with the use of MMI during the first trimester of pregnancy. The authors believe that PTU should not be used in pediatric patients unless the patient is allergic to or intolerant of MMI, and there are no other treatment options available. That being said, PTU may be the treatment of choice during, and just before, the first trimester of pregnancy.

Fetal outcome after technetium scintigraphy in early pregnancy

OBJECTIVE

Occasionally, either for urgent diagnostic reasons or by accident, pregnant women are exposed to technetium scintigraphy, the consequences of which were unknown, due to lack of systematic data. Therefore, clinical data was needed to assess the risk and safety of technetium scintigraphy with respect to prenatal development.

METHODOLOGY

Requests for information with regard to technetium scintigraphy from pregnant women or their physicians were followed by the Berlin Institute for Clinical Teratology. A prospective observational cohort study was performed using data collected between 1991 and 2008. Pregnancy outcome for a cohort of pregnant women exposed to Tc-99m-scintigraphy of thyroid (n=102) or bone (n=20) during pregnancy was compared with a control group without teratogenic exposure (n=366).

RESULTS

Major birth defects were no more common in the study group than in the control group (OR 1.00; 95% CI 0.23-3.38) and no specific pattern of birth defects was found. Spontaneous abortion rate (OR 0.51), preterm deliveries, and birth measurements of newborns were not significantly different from controls.

CONCLUSION

This prospective observational study suggests that the inadvertent exposure to Tc-99m-scintigraphy in early pregnancy is relatively safe for the fetus.

Asthma control during pregnancy and the risk of preterm delivery or impaired fetal growth

BACKGROUND

Concerns regarding potential harmful effect of medications on fetuses often result in inadequate treatment of asthma in pregnancy, whereas risks posed by poorly controlled maternal asthma are often underestimated.

OBJECTIVE

To evaluate the effect of maternal asthma on preterm delivery and fetal growth.

METHODS

Study participants were individuals enrolled in the Organization of Teratology Information Specialists Asthma Medications in Pregnancy Study between February 1, 1998, and December 31, 2003. Pregnant women with physician-diagnosed asthma (n = 719) evaluated their asthma control repeatedly during pregnancy based on symptom frequency and interference with daily activities and sleep and reported hospitalizations and unscheduled clinic visits for asthma exacerbations. The incidence of preterm delivery, the incidence of intrauterine growth restriction, and mean birth weight were evaluated relative to asthma symptom control and exacerbation measures.

RESULTS

The incidence of preterm delivery was significantly higher among patients with inadequate asthma symptom control during the first part of pregnancy (11.4%) compared with patients with adequate asthma control (6.3%; P = .02). Similarly, patients who were hospitalized for asthma during pregnancy had a higher incidence of preterm delivery (16.4%) compared with asthmatic women without a history of hospitalization (7.6%; P = .02). The effect seemed independent from use of systemic corticosteroids and other covariates. Neither the incidence of intrauterine growth restriction nor mean birth weight varied by any measures of asthma symptom control or exacerbations.

CONCLUSIONS

This study demonstrates a substantial risk for preterm delivery posed by poorly controlled maternal asthma and provides additional evidence regarding the importance of adequate treatment of asthma in pregnancy to maintain optimal asthma control.

Maternal use of fluconazole and risk of congenital malformations: a Danish population-based cohort study

OBJECTIVES

Fluconazole is widely used for the treatment of candidiasis. Although the drug is also prescribed to pregnant women, data on the safety of use of fluconazole during pregnancy are limited. We examined the association between the maternal use of fluconazole during pregnancy and the risk of congenital malformations.

PATIENTS AND METHODS

In this population-based cohort study in Northern Denmark, we included 1079 women who had a live birth or a stillbirth after the 20th week of gestation and who redeemed at least one prescription for fluconazole during the first trimester. The reference cohort comprised 170 453 pregnant women who redeemed no fluconazole prescription during pregnancy. The women were identified through the Danish Medical Birth Registry. Data on drug use, birth outcome and covariates were extracted from population-based healthcare databases. We used logistic regression to estimate the prevalence odds ratio (POR) for congenital malformations after fluconazole exposure, while adjusting for maternal smoking, parity, maternal age and concurrent prescriptions for antiepileptics or antidiabetics.

RESULTS

Among 1079 women who filled a fluconazole prescription during the first trimester, 797 (74%) received a total of 150 mg of fluconazole, 235 (22%) received 300 mg of fluconazole, 24 (2%) received 350 mg of fluconazole and 23 (2%) received 600 mg of fluconazole. These women gave birth to 44 (4.1%) children with congenital malformations. The 170 453 women without fluconazole prescriptions gave birth to 6152 (3.6%) children with congenital malformations. For congenital malformations overall, the adjusted POR associated with the first-trimester fluconazole use was 1.0 (95% confidence interval: 0.8-1.4).

CONCLUSIONS

We found no overall increased risk of congenital malformations after exposure to short-course treatment with fluconazole in early pregnancy.

Safety of leukotriene receptor antagonists in pregnancy

BACKGROUND

Asthma is a chronic disorder that affects about 8% of pregnant women and may complicate pregnancy. Adequate asthma therapy in pregnancy is crucial but challenging because of safety concerns for the fetus.

OBJECTIVE

To evaluate the safety of gestational asthma therapy with leukotriene receptor antagonists (LTRAs) for the mother and fetus/newborn.

METHODS

Subjects were participants of the Organization of Teratology Information Specialists Asthma Medications in Pregnancy Study. Perinatal outcomes among 96 women who took LTRAs (montelukast or zafirlukast) were compared with women who exclusively took short-acting beta(2)-agonists (n = 122) and women without asthma (n = 346).

RESULTS

Use of LTRAs was not associated with an increased risk of pregnancy loss, gestational diabetes, preeclampsia, low maternal weight gain, preterm delivery, low Apgar scores, or reduced measures of birth length and head circumference in infants (P > .05). Slightly decreased birth weight in infants born to LTRA users could be attributed to maternal asthma severity/control. The birth prevalence of major structural defects in the LTRA group (5.95%) was significantly higher compared with controls without asthma (P = .007), but not different from the comparison group with asthma (P = .524). Furthermore, the defects observed in the LTRA group did not represent a consistent pattern.

CONCLUSIONS

Use of LTRAs in pregnancy was not associated with a specific pattern of major structural anomalies in offspring or a large risk of other adverse perinatal outcomes.

CLINICAL IMPLICATIONS

This study suggests that LTRAs do not appear to be a major human teratogen; however, results should be interpreted with caution because of limited sample size.

Teratogenesis of sodium valproate

PURPOSE OF REVIEW

Sodium valproate has been a first-line antiepileptic drug for 40 years. A recent multicentre study conducted in the UK (Standard and New Antiepileptic Drugs) has confirmed what most practising neurologists had long suspected--that sodium valproate is the most effective drug in the treatment of idiopathic generalized epilepsy and juvenile myoclonic epilepsy.

RECENT FINDINGS

Knowledge of the drug's unsurpassed efficacy has intensified the dilemma faced by neurologists treating people with epilepsy, and in particular young women. Recent data from pregnancy registers has not only confirmed that sodium valproate is teratogenic but also that it may be associated with neurodevelopmental delay and autistic spectrum disorders in the children of women exposed to the drug during pregnancy. Thus physicians have to balance the undoubted benefits of seizure freedom for their female patients with the potential long-term consequences for the infants of these patients.

SUMMARY

There is undoubtedly a phamacogenetic component to sodium valproate's teratogenic and neurodevelopmental effects. Future research may enable us to identify those women whose offspring may be affected. Research now underway will help quantify the precise risk of neurodevelopmental delay in the offspring of women exposed to the drug, although it will be some years before results become available.

Linking teratogen information service and birth defects registry databases to improve knowledge of birth defect status

BACKGROUND

Although teratogen information services (TISs) obtain maternal exposure information from their callers, such services often do not know if the pregnancies were affected by a birth defect. This study attempted to improve the completeness of this information for Texas Teratogen Information Service (TTIS) callers by linking their records with the Texas Birth Defects Registry (TBDR) and Texas birth certificates (TBCs).

METHODS

A total of 344 expectant mothers called TTIS with expected dates of delivery between 1 January 2000 and 31 December 2001. These pregnancies were linked with TBDR and TBC data. The percentages of pregnancies with known birth defect information both before and after the linkage were compared.

RESULTS

The TTIS originally collected birth defect status information for 101 of the 344 callers (29.4%) and 0.6% of all 344 callers or 2.0% of callers with birth defect status information had a pregnancy affected by a birth defect. Linking TTIS records with TBDR and TBC data helped to raise the percentage of callers with birth defect status information from 29.4% to 71.5%. Among those callers, the percentage known to have birth defects increased from 2.0% to 4.1%. The sensitivity of TTIS follow-up calls in identifying birth defects was 50%, and the specificity was 100%.

CONCLUSIONS

Linking TTIS caller records with TBDR and TBC data significantly increased both the percentage of pregnancies with birth defect status information and the percentage of pregnancies identified as affected by birth defects. Such linkage may be a good approach by which TISs can increase the completeness of their birth defect status information.

The contribution of new findings and ideas to the old principles of teratology

Although the last generally accepted concept of principles of teratology was issued more than 30 years ago, the cause of less than 50% of all congenital anomalies is known and no substantial change in their incidence has been observed worldwide. In the meantime, powerful techniques of molecular biology as well as many sophisticated preventive measures have been introduced with marginal effects on the overall birth defects numbers. In this paper, we follow the history of basic concepts of teratology starting with Isidore Geoffroy Saint-Hilaire and Dareste, followed in the 20th century by James Wilson. Since that time no bright and completely new idea, which would deserve the name principle, has emerged. The advanced molecular studies support the long-existing principles and disclose the great variability of individuals and their responses to adverse exposures. In this way, the future of teratology counseling may be seen in a deep analysis of any individual case.

Methodological issues in the epidemiological study of the teratogenicity of drugs

The review presented here discusses and exemplifies problems in epidemiological studies of drug teratogenesis according to methodology: case-control studies, cohort studies, or total population studies. Sources of errors and the possibility of confounding are underlined. The review stresses the caution with which conclusions have to be drawn when exposure data are retrospective or other possible bias exists. It also stresses the problem with the multiple testing situation that is usually present in the studies. It is therefore difficult to draw any firm conclusion from single studies and still more difficult to draw conclusions on causality. As randomized studies are in most cases out of the question, one has to rely on the type of studies which can be made, but the interpretation of the results should be cautious. The ideal study, next to a randomized one, is a large prospective study with detailed exposure information and detailed and unbiased outcome data. Even so, such a study can mainly be used for identifying possible associations which have to be verified or rejected in new studies. Nearly every finding of a risk increase, if not extremely strong, should only be regarded as a tentative signal to be tested in independent studies.

Angiotensin II-receptor-antagonists: further evidence of fetotoxicity but not teratogenicity

BACKGROUND

Like angiotensin converting enzyme (ACE) inhibitors angiotensin II (AT II)-receptor-antagonists may cause persistent or even lethal fetotoxic defects when used during the late second or third trimester. There are insufficient data on first-trimester exposure to these substances in terms of teratogenicity. The two databases of the Berlin Teratology Information Service (TIS) were evaluated for pregnancy outcome following exposure to AT II-receptor-antagonists. One database covers case reports on newborns with congenital abnormalities identified after birth, in which drug-effect associations can be evaluated retrospectively. The other enrolls women prospectively according to exposure to particular drugs during pregnancy, with follow-up of pregnancy outcome.

CASES

Five cases (four retrospective and one prospective) involving late-pregnancy use of AT II-receptor-antagonists were recently reported to us, each of which included one or more of the following abnormalities: oligohydramnios/anhydramnios, anuria, hypoplastic skull bones, limb contractions, lung hypoplasia, and neonatal death. Among 37 prospectively enrolled first-trimester-exposed pregnancies there were 30 live births including one with a major malformation (cleft palate). One pregnancy was electively terminated after exencephaly had been diagnosed.

CONCLUSIONS

AT II-receptor-antagonists may induce fetotoxic effects when used in the second and third trimesters. The available data on first-trimester use do not strongly support a teratogenic potential. AT II-receptor-antagonists should not be used by pregnant women. In case of inadvertent exposure, therapy should be changed to the known antihypertensives of choice (e.g., metoprolol, methyldopa, and hydralazine) and fetotoxic effects should be ruled out by ultrasound. Treatment with AT II-receptor-antagonists during early pregnancy is not in itself an indication for termination of a wanted pregnancy.

Teratology Information Services in Europe and Their Contribution to the Prevention of Congenital Anomalies

OBJECTIVES

To inform on Teratology Information Services (TIS) in Europe, their history, function and activity in preventing congenital malformations.

CONCLUSIONS

Clinical teratology tries to identify human teratogens. TIS play an important role in public health by providing counsel on known reproductive risks and conducting specific research. This has led to a reduction in unnecessary fears of pregnant women and pregnancy terminations, as well as to better, more appropriate drug selection to treat acute or chronic disease. In addition, TIS units also conduct prospective studies and inform the public and physicians of the possible effects of environmental agents on the developing embryo and fetus.

Postmarketing surveillance for human teratogenicity: a model approach

BACKGROUND

Most congenital defects associated with prenatal exposures are notable for a pattern of major and minor malformations, rather than for a single major malformation. Thus, traditional epidemiological methods are not universally effective in identifying new teratogens. The purpose of this report is to outline a complementary approach that can be used in addition to other more established methods to provide the most comprehensive evaluation of prenatal exposures with respect to teratogenicity.

METHODS

We describe a multicenter prospective cohort study design involving dysmorphological assessment of liveborn infants. This design uses the Organization of Teratology Information Services, a North American network of information providers who also collaborate for research purposes. Procedures for subject selection, methods for data collection, standard criteria for outcome classification, and the approach to analysis are detailed.

RESULTS

The focused cohort study design allows for evaluation of a spectrum of adverse pregnancy outcomes ranging from spontaneous abortion to functional deficit. While sample sizes are typically inadequate to identify increased risks for single major malformations, the use of dysmorphological examinations to classify structural anomalies provides the unique advantage of screening for a pattern of malformation among exposed infants.

CONCLUSIONS

As the known human teratogens are generally associated with patterns of structural defects, it is only when studies of this type are used in combination with more traditional methods that we can achieve an acceptable level of confidence regarding the risk or safety of specific exposures during pregnancy.