- Little data exist on the safety of H(2)-blockers during pregnancy. A computerized database of medications dispensed from 1998 to 2007 to all women registered in the "Clalit" health maintenance organization, in the Southern District of Israel, was linked with computerized databases containing maternal and infant hospitalization records from the district hospital. The following confounders were controlled for: parity, maternal age, ethnic group, maternal diabetes, smoking, and peripartum fever. Also, therapeutic pregnancy termination data were analyzed. A total of 117 960 infants were born during the study period, 84 823 of them (72%) to women registered at Clalit; 1148 of the latter were exposed to H(2)-blockers during the first trimester of pregnancy. Exposure to H(2)-blockers was not associated with an increased risk for congenital malformations (adjusted odds ratio [OR] = 1.03, 95% confidence interval [CI]: 0.80-1.32); also, no such association was found when therapeutic pregnancy terminations were included in the analysis (adjusted OR = 1.17, 95% CI: 0.93-1.46). Exposure to H(2)-blockers was not associated with perinatal mortality, premature delivery, low birth weight, or low Apgar scores.