Should we treat mild gestational diabetes? An Australian multicentre retrospective cohort study

Aims: The International Association of Diabetes in Pregnancy Study Groups (IADPSG) diagnostic criteria for gestational diabetes (GDM) were widely implemented in Australia, despite limited evidence of better pregnancy outcomes compared to the Australasian Diabetes in Pregnancy Society 1998 (ADIPS1998) criteria. We aimed to evaluate the effect of treatment on pregnancy outcomes for women with ‘mild’ GDM, defined as GDM diagnosed by one, but not both, sets of criteria. Methods: This multicentre, retrospective cohort study included 17,512 pregnant women in six neighbouring tertiary hospitals in Sydney, Australia, during 2016–2017, all of whom were screened for GDM using a three-point 75 g oral glucose tolerance test. Three hospitals diagnosed and treated GDM according to ADIPS1998 criteria, and three according to IADPSG criteria. For women with ‘mild’ GDM, we evaluated the effect of treatment versus no treatment on pregnancy outcomes. The primary outcome was large for gestational age. Secondary outcomes were small for gestational age, induction of labour, caesarean section, gestational hypertension, and preeclampsia. Results: 2320 (13.2%) pregnant women had ‘mild’ GDM. Treatment of women with IADPSG-only GDM (i.e. fasting glucose 5.1–5.4 mmol/L (91–97 mg/dL) and/or 1-hour glucose ≥ 10.0 mmol/L (≥ 180 mg/dL)) was associated with less large for gestational age infants than no treatment (RR 0.66, 95%CI 0.49–0.88, p = 0.004) but more induction of labour (RR 1.55, 95%CI 1.03–2.34, p = 0.032). Treatment of women with ADIPS1998-only GDM (i.e. 2-hour glucose 8.0-8.4 mmol/L (144–151 mg/dL)) did not significantly change pregnancy outcomes compared with no treatment. Conclusions: This study highlights the importance of treating even mild IADPSG-GDM to improve pregnancy outcomes.