Background: Pregnancy registries are a new method for assessing the fetal risks from exposures in pregnancy. We present the findings of the North American AED (antiepileptic drug) Pregnancy Registry for phenobarbital sodium-exposed pregnancies.
Objective: To determine whether exposure during pregnancy to anticonvulsant drugs as monotherapy, and phenobarbital in particular, is associated with an increased risk of major malformations in comparison with unexposed controls.
Design: Evaluation of registry data.
Setting: The North American AED Pregnancy Registry.
Patients: Pregnant women throughout the United States and Canada who were taking an anticonvulsant drug and who called a toll-free telephone number to enroll.
Interventions: Each woman was interviewed by telephone at enrollment, at 7 months' gestation, and post partum. With the mother's written permission, her medical records and those of her infant were obtained.
Main outcome measures: Major malformations identified by 5 days of age. Criteria for the release of findings were established by the independent Scientific Advisory Committee on the basis of malformations identified in infants of women who had enrolled prospectively before having had any prenatal screening ("pure" enrollees).
Results: Five (6.5%) of 77 pure pregnancies with exposure to phenobarbital monotherapy were associated with major malformations (95% confidence interval of proportion, 2.1%-14.5%). When compared with the background rate (1.62%), there was a significantly increased risk (relative risk, 4.2; 95% confidence interval, 1.5-9.4).
Conclusions: A hospital-based pregnancy registry can establish the fetal risk of major malformations for a commonly used drug. Prenatal exposure to phenobarbital is associated with a significantly increased risk of fetal abnormalities.