Medications for Nausea and Vomiting of Pregnancy and the Risks for Adverse Birth Outcomes

Nausea and vomiting of pregnancy (NVP) is common during pregnancy. However, evidence on the safety of its treatment is still conflicting. This study compared the risk for adverse birth outcomes between mothers exposed to NVP medications and unmedicated mothers, with and without NVP.

This prospective, observational cohort study is part of the MotherToBaby Pregnancy Studies initiative, which recruits participants during pregnancy and collects data through maternal telephone interviews and medical records. The study includes live-born singleton pregnancies enrolled from 2010 to 2023, with available first-trimester NVP symptom data. Pregnant women exposed to any NVP medications were compared to pregnant women with untreated NVP and pregnant women without NVP. Statistical analysis involved calculating risk ratios (RR) for major congenital malformations, preterm delivery, small for gestational age (SGA), and admission to the neonatal intensive care unit (NICU).

This study included 2711 pregnant individuals, categorized into NVP treatment exposed (n = 603; mean [SD] age, 33.2 [4.3] years), untreated NVP (n = 1567; mean [SD] age, 33.3 [4.4] years), and no NVP (n = 541; mean [SD] age, 33.4 [4.4] years). Major congenital malformations occurred in 6.12% (n = 29) of the NVP treatment exposed group, 5.11% (n = 80) of the untreated NVP group, and 5.55% (n = 30) of the no NVP group, with adjusted RR for treatment exposed 1.22 (95% CI, 0.79-1.87) compared to untreated NVP and 1.05 (95% CI, 0.63-1.76) compared to no NVP. The adjusted RR of preterm birth was 1.21 (95% CI, 0.88-1.67) for treatment exposed compared to untreated NVP. The adjusted RR of infants being SGA was 1.25 (95% CI, 0.90-1.74) compared to untreated NVP. Doxylamine (n = 345 [57.21%]) and ondansetron (n = 286 [47.43%]) were the most commonly used NVP treatments. When the risks for adverse birth outcomes were evaluated separately for these medications, ondansetron exposure was associated with higher RRs for SGA compared with both untreated NVP (adjusted RR 1.80, 95% CI 1.23-2.60) and no NVP (1.99, 95% CI 1.22-3.24). The confidence intervals indicate that the estimates are relatively imprecise but suggest an increased risk in both comparisons.

No increased risks of major congenital malformations or other adverse birth outcomes were observed when comparing women treated with NVP medications to those with untreated NVP or no NVP, in overall comparisons, supporting the pharmacological treatment of NVP when needed. Ondansetron exposure was associated with an increased risk of SGA, which may at least partially be influenced by greater NVP severity among ondansetron-treated women rather than treatment effect itself.