Oral antidiabetic agent metformin and glyburide have shown efficacy with no evidence of harm to the foetus, although long-term safety remains a concern. Trials have shown that glyburide does not cross the placental barrier (94, 95) or may cross it in low concentrations (96) while metformin concentration is similar in the fetal and maternal circulation. In the Metformin in Gestational Diabetes (MiG) trial, the largest study of metformin use in women with GDM compared to insulin therapy (97). There was no significant difference in the fetal outcome between the two groups and approximately half of the metformin-treated mothers also required insulin in order to achieve target glucose levels. Nevertheless, metformin seems to be favourable with regards to weight gain and amount of insulin needed during pregnancy (9