The prognostic value of the oral glucose tolerance test for future type-2 diabetes in nulliparous pregnant women testing negative for gestational diabetes

Aim — To determine the prognostic value of the antepartum 75g-oral glucose tolerance test (OGTT) for future type 2 diabetes mellitus (T2DM) in nulliparous pregnant women who tested negative for GDM.

Methods — A population-based retrospective cohort study of nulliparous pregnant women who underwent testing for GDM using a 75g-OGTT in Ontario, Canada (2007-2017). The overwhelming majority of women in Ontario undergo screening using the preferred 2-step approach where the 75g-OGTT is performed following an abnormal non-fasting 1-hour 50g-glucose challenge test. The relationship between the 75g-OGTT results in women who tested negative for GDM (defined as normal glucose at fasting, 1 and 2 hours post 75g-glucose load) and future T2DM (as recorded in the Ontario Diabetes Database by the end date of follow up period) was explored.

Findings — Of the 162,622 women who underwent 75g-OGTT during the study period, there were 41,507 (75.0%) who met the study criteria. In women without GDM, the adjusted hazard ratios (aHR) for T2DM were: at fasting 2.82 (95%-CI 2.18-3.64), at 1-hour 1.26 (1.15-1.37), at 2-hours 1.14 (1.04-1.25) for a 1 mmol/l increase in glucose. A model that combined all 3 OGTT values and clinical characteristics could detect 43% (42.6%-43.4%) of those who developed T2DM at 5-years post the index pregnancy for a false-positive rate of 20%.

Interpretation — The results of the antepartum OGTT can be used to refine the future risk of T2DM even in nulliparous pregnant women who tested negative for GDM.