Random plasma glucose in early pregnancy is a better predictor of gestational diabetes diagnosis than maternal obesity

Aims: Asymptomatic pregnant women are screened for Gestational Diabetes (GDM) between 24-28 weeks gestation. Recent guidelines also recommend screening early in gestation to identify undiagnosed pre-existing overt diabetes. The study aim was to assess the performance of random plasma glucose (RPG) at antenatal booking to predict GDM diagnosis later in pregnancy.  Methods: Data from 25543 consecutive singleton pregnancies at the Rosie hospital in Cambridge (UK) were obtained from hospital electronic records as a service evaluation. All women were invited for an antenatal RPG (12-16 weeks) and a 50g glucose challenge test (GCT; 24-28 weeks) with 75g oral glucose tolerance test (OGTT) if GCT>7.7mmol/l (139mg/dl).  Results: 17736 women had RPG at booking which was able to predict GDM (ROC AUC 0.8) according to various diagnostic criteria in common use. A cut-off point of >7.5mmol/l (135mg/dl) gave a sensitivity of 70% and a specificity of 90% for GDM diagnosis. Theoretically, using this screening policy, 13.2% women would have been categorised at high risk (26.3% had GDM) and 86.8% women at low risk (1.7% had GDM). RPG performed better than maternal age (AUC 0.60) or body mass index (AUC 0.65) at predicting GDM diagnosis.  Conclusions: RPG at booking has reasonable performance as a screening test and is better than maternal age or BMI for identifying women at high risk of developing GDM. RPG cannot replace OGTT for diagnosis but it may be useful both for excluding women who do not need further investigation for GDM and for identifying women who could be prioritised for early diagnosis or lifestyle interventions