Maternal pre-pregnancy body mass index and the risk for gestational diabetes mellitus in women with twin pregnancy in South Korea

Objective: To investigate the association between maternal pre-pregnancy body mass index (BMI) and the risk for gestational diabetes mellitus (GDM) in women with twin pregnancy in South Korea. Materials and methods: We performed a single-center, retrospective cohort study involving 1028 women with twin pregnancy from January 2006 to December 2018 in South Korea. Pregnancies with monoamnionic twins, twin–twin transfusion syndrome, fetal death in utero before 24 weeks, pre-gestational diabetes mellitus, and unknown BMI or GDM status were excluded. Subjects were grouped into four groups based on pre-pregnancy BMI: underweight (<18.5 kg/m²), normal (18.5–22.9 kg/m²), overweight (23.0–24.9 kg/m²), and obese (≥25.0 kg/m²). Results: Among 1028 women who were included in the analysis, 169 (16.4%), 655 (63.7%), 111 (10.8%), and 93 (9.0%) women were underweight, normal, overweight, and obese, respectively, before pregnancy. The incidence of GDM was 8.9% in the total study population: 4.7%, 8.2%, 11.7%, and 17.2% in the underweight, normal, overweight, and obese group, respectively (p = 0.005). The incidence of GDM significantly increased according to the increase in pre-pregnancy BMI (p < 0.001). Women in the obese group were more likely to be affected by GDM compared to the normal group (adjusted odds ratio = 2.20, 95% confidence interval = 1.19–4.08) after controlling for maternal age, parity, type of conception, and chorionicity. Conclusion: In twin pregnancies in South Korea, the risk of GDM increased as maternal pre-pregnancy BMI increased and obese women before pregnancy were more likely to be affected by GDM.