Use of prescription drugs in the first trimester and congenital malformations.

A prospective survey of prenatal use of prescription drugs in Tasmania yielded detailed information on drug exposure, delivery and outcome for 56,037 births from 1982 to 1989. First trimester drug use was reported by 30.9% of women, and 17.9% used only supplements of vitamins and/or minerals; 40% used alcohol during the first trimester, and 28.8% smoked cigarettes. There were 1,035 (1.85%) congenital malformations, of which 885 (85.5%) were major. The malformation rate was not significantly different in the following exposure categories: supplements only (1.62%); other pharmaceuticals (1.92%); smokers (1.88%); alcohol users (1.89%); and maternal age 35 or more years (1.95%). Adjusting for alcohol use, smoking, maternal age and diabetes mellitus, significant associations [expressed as adjusted odds ratio and 95% confidence intervals (CI)] were found between aspirin and hypospadias (3.5, 95% CI 1.4 to 8.8); dicyclomine and phocomelia (4.4, 95% CI 1.0 to 19.5); and between oral contraceptive use and pes cavus (9.7, 95% CI 2.3 to 40.4). Although significant, these associations were based on very few cases and no direct supporting evidence could be found from other data sources.