Incidence and risk factors for gestational diabetes mellitus in twin versus singleton pregnancies

To compare the incidence and risk factors for gestational diabetes mellitus (GDM) between women with twin and singleton pregnancies. Retrospective study of all women who had a twin or singleton birth in Ontario (2012-2016). Risk ratios (RR) and 95% CIs for GDM (stratified by type of treatment) were adjusted for relevant confounding variables. Multivariable Poisson regression analysis was used to identify risk factors for GDM in twin and singleton gestations. Of 270,843 women who met inclusion criteria, 266,942 (98.6%) and 3901 (1.4%) had a singleton and a twin pregnancy, respectively. Women with twins had a significantly higher risk for overall GDM (aRR = 1.13, 95% CI 1.01-1.28) and diet-treated GDM (aRR = 1.20, 95% CI 1.01-1.42) while the association with insulin-treated GDM was not significant (aRR = 1.07, 95% CI 0.89-1.28). Maternal age 35 years, non-Caucasian ethnicity and BMI > 30 kg/m(2) were independent risk factors for GDM among women with twins and singletons, and the magnitude of the association of these factors with GDM was similar. Women with twins are at increased risk of GDM, mainly due to a higher rate of diet-treated GDM. Despite higher baseline risk of GDM in women with twins, the effect of known risk factors for GDM is similar to that observed in singletons.