Undiagnosed type 2 diabetes during pregnancy is associated with increased perinatal mortality: a large population-based cohort study in Ontario, Canada.

AIM: To compare perinatal outcomes in women with undiagnosed diabetes with gestational diabetes alone, pre-existing diabetes and women without diabetes, and to identify risk factors which distinguish them from women with gestational diabetes alone.

METHODS: This population-based cohort study included administrative data on all women who gave birth in Ontario, Canada, during 2002-2015. Maternal/neonatal outcomes were compared across groups using logistic regression, adjusting for confounders. A nested case control study compared women with undiagnosed type 2 diabetes with women with gestational diabetes alone to determine risk factors that would help identify these women.

RESULTS: Among 995 990 women, 68 163 had gestational diabetes (6.8%) and, of those women with gestational diabetes,1772 had undiagnosed type 2 diabetes (2.6%). Those with undiagnosed type 2 diabetes were more likely to be older, from a lower income area, have parity > 3 and BMI ≥ 30 kg/m2 compared with gestational diabetes alone. Infants had a higher risk of perinatal mortality (OR 2.3 [1.6-3.4]), preterm birth (OR 2.6 [2.3-2.9]), congenital anomalies (OR 2.1 [1.7-2.5]), neonatal intensive care unit admission (OR 3.1 [2.8-3.5]) and neonatal hypoglycaemia (OR 406.0 [357-461]), which were similar to women with pre-existing diabetes. The strongest predictive risk factors included early gestational diabetes diagnosis, previous gestational diabetes and chronic hypertension.

CONCLUSIONS: Women diagnosed with gestational diabetes who develop diabetes within 1 year postpartum are at higher risk of adverse pregnancy outcomes, including perinatal mortality. This highlights the need for earlier diagnosis, preferably pre-pregnancy, and more aggressive treatment and surveillance of suspected type 2 diabetes during pregnancy.