Aims/hypothesis: This study aimed to determine the characteristics and pregnancy outcomes across different subtypes of gestational diabetes mellitus (GDM) based on insulin resistance.

Methods: GDM subtypes were defined in 1813 pregnant women from a multicentre prospective cohort study, stratified according to insulin resistance, based on Matsuda index below the 50th percentile of women with normal glucose tolerance (NGT), during a 75 g OGTT at 24-28 weeks' gestation. GDM was diagnosed in 12.4% (n = 228) of all participants based on the 2013 WHO criteria.

Results: Compared with women with NGT (1113 [61.4%] of the total cohort) and insulin-sensitive women with GDM (39 [17.1%] women with GDM), women with GDM and high insulin resistance (189 [82.9%] women with GDM) had a significantly higher BMI, systolic BP, fasting plasma glucose (FPG), fasting total cholesterol, LDL-cholesterol and triacylglycerol levels in early pregnancy. Compared with women with NGT, insulin-sensitive women with GDM had a significantly lower BMI but similar BP, FPG and fasting lipid levels in early pregnancy. Compared with women with NGT, women with GDM and high insulin resistance had higher rates of preterm delivery (8.5% vs 4.7%, p = 0.030), labour induction (42.7% vs 28.1%, p < 0.001), Caesarean section (total Caesarean sections: 28.7% vs 19.4%, p = 0.004; emergency Caesarean sections: 16.0% vs 9.7%, p = 0.010), neonatal hypoglycaemia (15.4% vs 3.5%, p < 0.001) and neonatal intensive care unit admissions (16.0% vs 8.9%, p = 0.003). In multivariable logistic regression analyses using different models to adjust for demographics, BMI, FPG, HbA_1c, lipid levels and gestational weight gain in early pregnancy, preterm delivery (OR 2.41 [95% CI 1.08, 5.38]) and neonatal hypoglycaemia (OR 4.86 [95% CI 2.04, 11.53]) remained significantly higher in women with GDM and high insulin resistance compared with women with NGT. Insulin-sensitive women with GDM had similar pregnancy outcomes as women with NGT. The need for insulin treatment during pregnancy and the rate of glucose intolerance in the early postpartum period were not significantly different among the GDM subtypes.

Conclusions/interpretation: GDM with high insulin resistance represents a more adverse metabolic profile with a greater risk of adverse pregnancy outcomes.