Diabetes mellitus is a common complication of pregnancy. The incidence of gestational diabetes mellitus (GDM) has steadily increased over recent years in comparison to that of type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM), which has remained stable. Our objective was to compare obstetric and neonatal outcomes of pregnancies complicated by diabetes mellitus by type of diabetes mellitus, to help inform current evidenced-based antenatal guidelines.
A retrospective cohort study of all pregnancies at the Royal Women’s Hospital, Melbourne, between 2010-2015, was performed to identify pregnancies complicated by diabetes mellitus. Demographic data, obstetric outcomes and neonatal outcomes were compared.
Of the 23,030 pregnancies occurring during the study period, ten percent were complicated by diabetes mellitus (3,203). Of this ten percent, 6.8% had T1DM, 7% had T2DM and the remaining 86.3% had GDM. Pre-existing diabetes was more commonly associated with hypertensive disease (18% T1DM, 20% T2DM, 7% GDM) and delivery at an earlier mean gestational age (36.0 weeks T1DM, 36.7 weeks T2DM, 37.8 weeks GDM). Caesarean section was more common in pre-existing diabetes (66% T1DM, 54% T2DM, 40% GDM). Mean birthweight at delivery was significantly greater in T1DM (3,328g T1DM, 3,100g T2DM, 3,152g GDM), and the incidence of macrosomia was also significantly increased in this group (20% T1DM, 9% T2DM, 5.9% GDM). The rate of stillbirth was significantly increased in pre-existing diabetes (2.3% T1DM, 4% T2DM, 0.9% GDM).
Pregnancies in women with pre-existing diabetes are associated with significantly worse outcomes compared to women with GDM. Both T1DM and T2DM should both be considered a significant risk factor for adverse pregnancy outcomes. Antenatal guidelines for the management of pre-existing diabetes, compared to GDM, should reflect the differing risk profile of these conditions.