Incidence of gestational diabetes mellitus diagnosed before 20 weeks of gestation

The objectives of this study were to determine the incidence of gestational diabetes mellitus (GDM) before 20 weeks of gestation and evaluate associated risk factors. A total of 1200 pregnant women who started their antenatal care at Siriraj Hospital before 20 weeks of gestation and were at risk of developing GDM were enrolled. A 50-gram glucose challenge test was used as a screening method and 100-gram oral glucose tolerance test was used to diagnose the condition. All women were screened during their first visit and again at 28-32 weeks of gestation. The results showed that the incidence of GDM diagnosed before 20 weeks of gestation was 5.3% (95% CI 4.1-6.7%), and another 4.9% were diagnosed during 28-32 weeks. This demonstrated the usefulness and effectiveness of the current guideline for GDM screening that approximately half of women with GDM could be diagnosed early in their pregnancies. The 2 independent risks for developing GDM before 20 weeks of gestation were age ≥ 30 years and GDM in previous pregnancy (adjusted OR 2.5, 95% CI 1.3-5.0, and 7.1, 95% CI 1.8-27.6, respectively). This specific group of women should be counseled regarding the importance of early GDM screening during their pregnancy.