Prevention of gestational diabetes by metformin plus diet in patients with polycystic ovary syndrome

Objective: To prospectively assess whether metformin diet safely provides primary and secondary prevention of gestational diabetes (GD). Design: Assess development of GD on metformin diet. Setting: Outpatient clinical research center. Patient(s): One hundred forty-two nondiabetic women with polycystic ovary syndrome (PCOS) who had at least one live-birth (LB) pregnancy on metformin diet (172 pregnancies, 180 LBs). Intervention(s): Women were given 26% protein, 44% carbohydrate diets, without calorie restriction during pregnancy. Metformin (2-2.55 g/d) was given preconception, through pregnancy. Main Outcome Measure(s): Development of GD. Result(s): On metformin, GD developed in 12 (7%) of 172 LB pregnancies. Forty-seven women had at least one previous LB pregnancy (n = 64) without metformin, with GD developing in 19 (30%). Subsequently, on metformin, these 47 women had 50 LB pregnancies, developing GD in 6 (12%), which was a statistically significant difference. Of 15 women who had previous GD without metformin, GD developed in 5 (31%) of 16 subsequent pregnancies on metformin. Of 32 women who were previously free of GD without metformin, GD developed in 1 (3%) of 34 subsequent pregnancies on metformin. Previous GD without metformin was the only statistically significant explanatory variable for current GD on metformin. Conclusion(s): Metformin diet during pregnancy in women with PCOS facilitates primary and secondary prevention of GD.