Metformin is widely used in the management of gestational diabetes mellitus (GDM). The major toxicity from the use metformin is lactic acidosis. Metformin increases lactate accumulation by inhibiting conversion of glucose from lactate and inhibiting gluconeogenesis from lactate. We present two cases of metformin induced acidosis in GDM women.

Case 1 34 year old who was G7P3 was started on metformin 500mg twice daily from 21 weeks gestation for gestational diabetes and later increased to 1g twice daily from 23 weeks gestation. Decision for elective caesarean section was planned for 37 weeks in view of fetal macrosomia with accelerated growth and polyhydramnios. During administration of steroids with sliding scale patient developed euglycaemic ketoacidosis, with bicarbonate level 12mmol/L and lactate level 3.03mmol/L. She was treated with intravenous fluid resuscitation. Her baby was delivered with cord pH 7.12 (arterial) and 7.15 (venous).

Case 2 32 year old primigravida who was started on metformin 500mg once a day at 31weeks 6 days for GDM, and was increased to 1g once a day a week later. She was induced at 38 weeks 6 days with propess. During labour she developed 4+ ketones with normal blood glucose. Her venous bicarbonate was 13mmol/L and lactate was 4.2mmol. Fetal heart monitoring remained normal. She received fluid resuscitation which resolved her acidosis level. She delivered a healthy baby two hours after the onset of ketoacidosis.

Summary Our case reports have demonstrated the need to have high index of suspicion for ketoacidosis when managing GDM women on metformin.