One in six live births occur in women with diabetes mellitus, of which the most common type, accounting for approximately 87.5% of all diabetes in pregnancy, is gestational diabetes mellitus (GDM). Maternal hyperglycaemia is one of the principle determinants of maternal–fetal complications in pregnancy in GDM. In particular, hyperglycaemia is most commonly associated with increased rates of instrumental and/or operative delivery, pre-eclampsia, increased adiposity, macrosomia and infant birthweight >90th percentile.