Original Article: Treatment Pregnancy outcomes in women with gestational diabetes treated with metformin or insulin: a case–control study J. Balani, S. L. Hyer, D. A. Rodin and H. Shehata* Diabetes Centre and *Maternal Medicine Unit, Epsom and St Helier University Hospitals NHS Trust, Carshalton, Surrey, UK Accepted 8 June 2009 Abstract Aims To compare maternal and neonatal outcomes in women with gestational diabetes mellitus (GDM) treated with either metformin or insulin. Methods One hundred and twenty-seven women with GDM not adequately controlled by dietary measures received metformin 500 mg twice daily initially. The dose was titrated to achieve target blood glucose values. Pregnancy outcomes in the 100 women who remained exclusively on metformin were compared with 100 women with GDM treated with insulin matched for age, weight and ethnicity. Results There were no significant differences in baseline maternal risk factors. Women treated with insulin had significantly greater mean (sem) weight gain from enrolment to term (2.72 Æ 0.4 vs. 0.94 Æ 0.3 kg; P < 0.001). There was no difference between the metformin and insulin groups, respectively, comparing gestational hypertension (6 vs. 7%, P = 0.9), pre-eclampsia (9 vs. 2%, P = 0.06) induction of labour (26 vs. 24%, P = 0.87) or rate of Caesarean section (48 vs. 52%, P = 0.67). No perinatal loss occurred in either group. Neonatal morbidity was improved in the metformin group; prematurity (0 vs. 10%, P < 0.01), neonatal jaundice (8 vs. 30%, P < 0.01) and admission to neonatal unit (6 vs. 19%, P < 0.01). The incidence of macrosomia (birthweight centile > 90) was not significantly different [metformin (14%) vs. insulin (25%); P = 0.07]. Conclusions Women with GDM treated with metformin and with similar baseline risk factors for adverse pregnancy outcomes had less weight gain and improved neonatal outcomes compared with those treated with insulin. Diabet. Med. 26, 798–802 (2009) Keywords gestational diabetes, metformin, pregnancy Abbreviations GDM, gestational diabetes; HBGM, home blood glucose monitoring; MiG, Metformin in Gestational Diabetes Introduction The prevalence of gestational diabetes (GDM) is increasing as the pregnant population becomes older and more obese [1,2]. The increase in GDM poses a significant risk for mother and child [3,4]. Furthermore, recent evidence from the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study shows that hyperglycaemia below diagnostic levels for diabetes is similarly associated with adverse pregnancy outcomes [5]. The benefit of treatment of GDM has been clarified in recent landmark studies. Lifestyle, diet and, when indicated, insulin, clearly improve outcomes in GDM [6]. Evidence of benefit has recently been extended to include women traditionally viewed as having impaired glucose tolerance (2-h glucose value of > 7.8 and < 11.1 mmol / l in an oral glucose tolerance test). These women, when actively managed as GDM rather than as normal pregnancies, have reduced rates of macrosomia and fewer serious perinatal outcomes [7]. Whilst effective, insulin has several disadvantages: the need for injections, the risk of hypoglycaemia, excessive weight gain and the costs involved (including specialist nurse time for education). A safe and effective oral agent would offer advantages over insulin and may well prove more acceptable to patients [8]. Metformin, by reducing insulin resistance, is a rational option for women with GDM. Evidence from the Metformin in Gestational Diabetes (MiG) trial showed that, compared with insulin, metformin was not associated with increased perinatal complications although an increase in spontaneous preterm Correspondence to: Dr Steve Hyer, Doreen Kouba Diabetes Centre, St Helier Hospital, Wrythe Lane, Carshalton, Surrey, SM5 1AA, UK. E-mail: steve.hyer@esth.nhs.uk DIABETICMedicine DOI: 10.1111/j.1464-5491.2009.02780.x ª 2009 The Authors. 798 Journal compilation ª 2009 Diabetes UK. Diabetic Medicine, 26, 798–802