This nationwide population-based study was carried out in Taiwan with the aim of comparing the risk of adverse pregnancy outcomes in women who received zolpidem treatment for insomnia during pregnancy with that in women who did not. The adverse outcomes identified and assessed were delivery of low-birth-weight (LBW) infants, preterm deliveries, delivery of small-for-gestational-age (SGA) infants, delivery of infants with congenital anomalies, and cesarean delivery. The incidences of these were compared between the groups after adjusting for other characteristics of the mothers and infants. The study used the Taiwan National Health Insurance Research Dataset (NHIRD) and birth-certificate registry. In total, the data from 2,497 mothers who received zolpidem treatment during pregnancy and those from 12,485 randomly selected mothers who did not receive the drug were included in the analysis. The results show that the adjusted odds ratios (ORs) for adverse pregnancy outcomes--LBW infants, preterm deliveries, SGA infants, and cesarean delivery--were all higher in mothers who received zolpidem treatment during pregnancy, relative to the randomly selected controls (1.39 (95% confidence interval (CI) = 1.17-1.64), 1.49 (95% CI = 1.28-1.74), 1.34 (95% CI = 1.20-1.49), and 1.74 (95% CI = 1.59-1.90), respectively). In conclusion, the risk of adverse pregnancy outcomes was higher in women who received zolpidem during pregnancy than in those who did not.