Maternal obesity in singleton versus twin gestations: a population-based matched case-control study

Objective: To examine the impact of pre-pregnancy obesity on adverse outcomes in twin compared to singleton pregnancies. Methods: Dichorionic twin gestations with maternal body mass index430 were matched to three singleton controls. Both obese groups were matched (1: 3) with non-obese controls. Rates of preeclampsia, gestational diabetes, cesarean section, and preterm birth were compared. Results: One hunder eighty-nine dichorionic twin pregnancies in obese mothers were matched to 567 twin pregnancies in non-obese mothers, and to 567 singleton pregnancies in obese mothers. The latter were matched to 1701 non-obese mothers with singletons. Preeclampsia was more common in obese mothers with both twins and singletons (odds ratio (OR) 3.95, 95% confidence interval (CI) 2.18-7.16 and OR 6.53, 95% CI 3.75-11.4, respectively) as was gestational diabetes (OR 4.35, 95% CI 2.18-8.69; OR 5.53 95% CI 3.60-8.50). Obese mothers with singletons were more likely to deliver abdominally, but the cesarean rates were obesity independent in twins. Obese mothers were more likely to deliver at534 weeks in both twin and singleton groups (OR 1.65, 95% CI 1.10-2.48, and OR 2.41, 95% CI 1.21-4.77, respectively). Conclusion: Obesity-attributable adverse outcomes are lower in twins compared to singletons. Obesity increases the risk of preterm birth regardless of plurality.