Oral contraceptives and birth defects.

This report compares the history of oral contraceptive (OC) use for 715 New York state women who gave birth to malformed infants with the history for a group of 715 matched controls who gave birth to normal children. The case mothers were found to have used the OC after last menstrual period (LMP), or just before conception, slightly more often than the controls. Confidence intervals for the relative risk estimates were wide, and were significantly higher than 1.0 only among the group of women whose children had one or more major structural or anatomical malformations. Cytogenetic abnormalities and hypospadias were not associated with OC use around or after the time of conception. For women who had children with major anatomical or structural malformations, the association with OCs was stronger among the older age group. The authors found no evidence of an increased risk among women who had conveived their child after one or more pill-free menstrual cycles. Several reported studies, including this one, show a predominance of males among malformed offspring whose mothers used OCs during pregnancy. These findings indicate that the association between birth defects and OC use around the time of conception is not large, but the association is not easily reconciled with a non-causal explanation.