Obstetric and neonatal outcomes of gestational diabetes mellitus in twin pregnancies according to changes in its diagnostic criteria from National Diabetes Data Group criteria to Carpenter and Coustan criteria: a retrospective cohort study

Background To compare obstetric and neonatal outcomes in twin pregnancies with or without gestational diabetes mellitus (GDM) before and after changes in GDM diagnostic criteria. Methods This was a retrospective cohort study of 1,764 twin pregnancies including 130 women with GDM (GDM group) and 1,634 women without GDM (non-GDM group). Patients with pregestational diabetes, unknown GDM status, and fetal death at < 24 gestational weeks were excluded. Obstetric and neonatal outcomes were compared between the two groups by two periods: period 1 (1995-2005) and period 2 (2005-2018) when National Diabetes Data Group criteria and Carpenter and Coustan criteria were used for diagnosis of GDM, respectively. Results The incidence of GDM in twin pregnancies increased from 4.0% in period 1 to 9.3% in period 2. Composite obstetric complications rate was significantly higher in the GDM group than that in the non-GDM group during period 1 (72.0% vs. 45.5%, P = 0.009). However, it became comparable during period 2 (60.0% vs. 57.4%, P = 0.601). Interaction between GDM and period indicated a significant differential effect of GDM by period on the rate of composite obstetric complications. The rate of composite neonatal complications was similar between the two groups during both periods. The interaction between GDM and period was not significant. Conclusion After changes of GDM diagnostic criteria, the incidence of GDM increased more than twice, and the rate of composite obstetric complications decreased, but the rate of composite neonatal complications did not change significantly.