Glycemia and Its Relationship to Outcomes in the Metformin in Gestational Diabetes Trial

OBJECTIVE: To determine how glucose control in women with GDM treated with metformin and/or insulin influenced pregnancy outcomes. RESEARCH DESIGN AND METHODS: Women randomly assigned to metformin or insulin treatment in the Metformin in Gestational Diabetes (MiG) trial had baseline glucose tolerance test (OGTT) results and A1C documented, together with all capillary glucose measurements during treatment. In the 724 women who had glucose data for analysis, tertiles of baseline glucose values and A1C and of mean capillary glucose values during treatment were calculated. The relationships between maternal factors, glucose values, and outcomes (including a composite of neonatal complications, preeclampsia, and large-for-gestational-age [LGA] and small-for-gestational-age infants) were examined with bivariable and multivariate models. RESULTS: Baseline OGTT did not predict outcomes, but A1C predicted LGA infants (P = 0.003). During treatment, fasting capillary glucose predicted neonatal complications (P < 0.001) and postprandial glucose predicted preeclampsia (P = 0.016) and LGA infants (P = 0.001). Obesity did not influence outcomes, and there was no interaction between glycemic control, randomized treatment, or maternal BMI in predicting outcomes. The lowest risk of complications was seen when fasting capillary glucose was <4.9 mmol/l (mean ± SD 4.6 ± 0.3 mmol/l) compared with 4.9–5.3 mmol/l or higher and when 2-h postprandial glucose was 5.9–6.4 mmol/l (6.2 ± 0.2 mmol/l) or lower. CONCLUSIONS: Glucose control in women with gestational diabetes mellitus treated with metformin and/or insulin is strongly related to outcomes. Obesity is not related to outcomes in this group. Targets for fasting and postprandial capillary glucose may need to be lower than currently recommended.