Comment: The quality of evidence is upgraded by large magnitude of effect.
In a population-based, retrospective cohort study 15 381 women referred for an antepartum oral glucose tolerance test (OGTT) indicative of an abnormal 50-g glucose challenge test (GCT), but without GDM, were matched (for age, region, socioeconomic status, and year of delivery) with up to 4 other women without such referral (n = 61 237). The two cohorts were followed over a median 6.4 years for the development of diabetes. The rate of incident DM was 5.04 cases per 1000 person-years in the cohort of women who underwent an antepartum OGTT, compared with 1.74 cases per 1000 person-years in women without an OGTT. The hazard ratio for subsequent DM in women with abnormal GCT was 2.56 (95% CI 2.28 to 2.87, P < 0.0001).