AbstractTo test the effect of maternal habits and home exposures during early pregnancy on the occurrence of congenital heart disease in the offspring, 406 cases and 756 controls were studied. The cases included all cardiovascular malformations detected in Finland during 1982–1983, while the healthy controls were randomly selected from all babies born during the same period. Case and control mothers were interviewed after delivery using a structured and pre‐tested questionnaire.Maternal overall drug consumption during the first trimester was as prevalent among case mothers (13.3%) as controls (14.6%). Neither was the risk of congenital heart disease associated with maternal use of contraceptive pills, salicylates, diazepam, or sweetening agents separately. Maternal exposures to disinfectants, dyes, lacquers, paints, pesticides, or glues at home were equally prevalent in case and control groups.Several earlier miscarriages was a predictor of an infant born with congenital heart disease (OR = 2.7, CI95= 1.4–5.3). Maternal ultrasound examination was performed during the first 16 weeks of pregnancy more often among the case group (28.3%) than among the control group (22.0%). However, the association between ultrasound examination and the risk of congenital heart disease in the offspring was not statistically significant (OR = 1.2, 95% confidence interval 0.9–1.7) when adjusted for confounding factors such as the threat of miscarriage in logistic regression analysis.It is concluded that maternal ultrasound examination, intake of some common drugs, and exposure to a number of environmental factors at home during early pregnancy are probably not harmful for the developing fetal heart. © 1992 Wiley