Off-Label Use of Ondansetron in Pregnancy in Western Australia

Nausea and vomiting of pregnancy is the most common medical condition in pregnancy. There is an increasing trend to prescribe ondansetron although its safety for use in pregnancy has not been established. Methods. Exposed pregnancies were all births in Western Australia, 2002-2005, where the mother was dispensed ondansetron under the Australian Pharmaceutical Benefits Scheme, compared with all other births during the same period. Outcomes investigated include maternal and child characteristics, birth defects, pregnancy, and delivery characteristics. Results. There were 96,968 births from 2002 to 2005. Ondansetron was dispensed to 251 pregnant women during this period. The women dispensed ondansetron were more likely to be privately insured (OR: 5.8; 95% CI: 4.3-7.9), to be Caucasian (3.3; 1.9-5.7), not to smoke during their pregnancy (2.9; 1.8-4.7), to have a multiple birth (2.7; 1.5-5.0), and to have used fertility treatment (1.8; 1.0-3.4). There was a small but not significantly increased risk of a major birth defect with first trimester exposure (1.2; 0.6-2.2). Conclusions. Our study did not detect any adverse outcomes from the use of ondansetron in pregnancy but could not conclude that ondansetron is safe to use in pregnancy.