OBJECTIVE A prospective study of the impact of obesity on pregnancy outcome in glucose-tolerant women. RESEARCH DESIGN AND METHODS The Irish Atlantic Diabetes in Pregnancy network advocates universal screening for gestational diabetes. Women with normoglycemia and a recorded booking BMI were included. Maternal and infant outcomes correlated with booking BMI are reported. RESULTS A total of 2,329 women fulfilled the criteria. Caesarean deliveries increased in overweight (OW) (odds ratio 1.57 [95% CI 1.24-1.98]) and obese (OB) (2.65 [2.03-3.46]) women. Hypertensive disorders increased in OW (2.30 [1.55-3.40]) and OB (3.29 [2.14-5.05]) women. Reported miscarriages increased in OB (1.4 [1.11-1.77]) women. Mean birth weight was 3.46 kg in normal BMI (NBMI), 3.54 kg in OW, and 3.62 kg in OB (P < 0.01) mothers. Macrosomia occurred in 15.5, 21.4, and 27.8% of babies of NBMI, OW, and OB mothers, respectively (P < 0.01). Shoulder dystocia occur in 4% (>4 kg) compared with 0.2% (<4 kg) babies (P < 0.01). Congenital malformation risk increased for OB (2.47 [1.09-5.60]) women. CONCLUSIONS OW and OB glucose-tolerant women have greater adverse pregnancy outcomes.