To investigate the effects of raised maternal BMI on pregnancy outcome in glucose tolerant women, using the IADPSG criteria. Prospective observational study of fetal and maternal outcome in a cohort of pregnant women recruited to a universal screening programme for gestational diabetes under the ATLANTIC-DIP partnership. Maternal outcomes included glucose, delivery mode, pregnancy induced hypertension (PIH), preeclampsia (PET), antepartum hemorrhage (APH) and postpartum hemorrhage (PPH). Fetal outcomes included birthweight, congenital malformation, fetal death, neonatal jaundice, hypoglycemia and respiratory distress. Increasing maternal BMI was associated with adverse pregnancy outcomes: higher cesarean section rates, pre-eclamptic toxemia, pregnancy induced hypertension, increased birth weight and congenital malformation. There was also an association between normal range glucose and emergency cesarean section, hypertension of pregnancy and birthweight. In spite of tightening criteria for hyperglycemia during pregnancy, raised BMI is associated with adverse pregnancy outcome.