Prevalence of false positive 50-g glucose challenge test in risk-based screening before 20 weeks of gestation and relationship with adverse pregnancy outcomes

Objectives: To determine the prevalence of false positive results of 50-g glucose challenge test (GCT) in risk-based screening before 20 weeks of gestation and relationship with pregnancy outcomes. Materials and Methods: A total of 500 singleton pregnancy who were at risk for gestational diabetes mellitus (GDM) and received 50-g GCT for GDM screening before 20 weeks of gestation were included. Women with abnormal 50-g GCT received 100-g OGTT for GDM diagnosis. Prevalence of false positive results of 50-g GCT and GDM were estimated. Various baseline characteristics and pregnancy outcomes were compared between groups. Results: Mean age was 33.4 ± 4.9 years, mean Body mass index (BMI) was 22.9 ± 4.4 kg/m2, and 45.6% were nulliparous. Common GDM risks were age ≥ 30 years (81.6%), family history of diabetes mellitus (DM) (30.4%), and overweight/obesity (24.6%). Mean gestational age at GDM screening was 9.8 ± 3.9 weeks. Normal 50-g GCT was found in 243 women (48.6%), 187 women (37.4%) had false positive GCT, and 70 women (14%) had GDM. Women with GDM had significantly higher age, BMI, and more likely to be overweight or obese than others (p < 0.05). Gestational weight gain was comparable between normal and false positive GCT but it was significantly greater than GDM (p < 0.001). A significant trend of increasing in the rate of large for gestational age (LGA) was observed in normal GCT, false positive GCT, and GDM group (14.4%, 21.9%, and 25.7%, respectively, p = 0.013). Logistic regression analysis showed that false-positive GCT and GDM independently increased the risk of LGA (adjusted odds ratio 1.76, 95% confidence interval 1.05-2.94, and 2.15, 95% confidence interval 1.1- 4.23). Conclusion: Prevalence of false positive GCT was 37.4%. False-positive GCT and GDM independently increased risk of LGA.