Pregnancy outcomes following systemic prenatal acyclovir exposure: Conclusions from the international acyclovir pregnancy registry, 1984-1999.

Background: Oral acyclovir is commonly used for genital herpes and other herpesvirus infections. Data on potential fetal risk are extremely limited. From 1984 to 1998, the Acyclovir in Pregnancy Registry monitored birth outcomes of women exposed to oral or intravenous acyclovir during pregnancy. This report describes the final results.

Methods: The registry was publicized to health care providers most likely to diagnose pregnancy; providers called the registry telephone number, then mailed in a brief questionnaire. Pregnancy outcomes were categorized either as outcomes with birth defects or outcomes without birth defects, subcategorized as live births, spontaneous pregnancy losses (including stillbirths), and induced abortions. Birth defects were defined using a modification of the CDC definition for birth defects surveillance systems. Observed rates were compared to the rate (3.2%) of birth defects expected in the general population.

Results: Between June 1, 1984 and June 30, 1998, 1695 pregnancies exposed to oral or IV acyclovir were registered; 461 (27%) were lost to follow-up. A total of 1234 pregnancies in 24 countries were followed, with a total of 1246 outcomes. Among 1246 pregnancy outcomes, 756 involved acyclovir exposure in the first trimester, 197 in the second trimester, and 291 in the third trimester. Among live births with first trimester acyclovir exposure, risk of birth defects was 19 of 596 (3.2%; 95% CI, 2.0-5.0%). No unusual defects or pattern of defects were apparent.

Conclusions: The observed rates and types of birth defects for pregnancies exposed to acyclovir did not differ significantly from those in the general population. Birth Defects Research (Part A), 2004. Published 2004 Wiley-Liss, Inc.