An oral glucose tolerance test in pregnancy can serve as a valuable predictor for future diabetes.

Background: Adherence to screening following a pregnancy with gestational diabetes mellitus (GDM) remains low.

Objective: To assess the risk of future type 2 diabetes (T2D) based on the number and type of abnormal results of a 100-gram oral glucose tolerance test (OGTT) performed during pregnancy.

Study design: This retrospective study used data from a major Israeli healthcare provider. Women aged 20 to 50 years without a prior diagnosis of T2D who had a complete 100-gram OGTT during their last pregnancy between January 2000 and December 2022 were included. The primary outcome was the development of T2D by September 2024. Risk was assessed using Cox proportional hazards models based on the number and type of abnormal OGTT values.

Results: The study included 107,889 women (age 34.1±5.2 years; BMI 27.6±5.3 kg/m²). Median follow-up was 6.7 years (IQR 3.3-12.4), totaling 900,000 person-years. T2D developed in 4,500 women (0.5%). When compared to women with all OGTT values normal, the risk of T2D rose with each additional abnormal value: hazard ratio (HR) 3.45 (95% CI: 3.15-3.77) for one abnormal value, 4.03 (3.69-4.41) for two, 7.15 (6.49-7.88) for three, and 10.60 (9.28-12.20) for four. Abnormal fasting glucose was associated with a higher risk (HR 5.28; 95% CI: 4.83-5.76) than abnormal non-fasting values (HR 3.03; 95% CI: 2.78-3.29). A previous diagnosis of GDM was significantly associated with future T2D risk, even in patients with no current abnormal OGTT values.

Conclusions: The number and type of abnormal OGTT results strongly predict future T2D. These findings can inform targeted postpartum interventions and predictive tools for early prevention in high-risk women.