OBJECTIVE - The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study found strong associations between higher levels of maternal glucose at 24-32 weeks, within what is currently considered normoglycemia and adverse pregnancy outcomes. Our aim was to evaluate the associations between first-trimester fasting plasma glucose level and adverse pregnancy outcomes. RESEARCH DESIGN AND METHODS - Charts of all patients who delivered at our hospital between June 2001 and June 2006 were reviewed. Only subjects with singleton pregnancy and a recorded first-trimester fasting glucose level were included. Women with pregestational diabetes, fasting glucose level >105 mg/dl, or delivery <24 weeks were excluded. Fasting glucose levels were analyzed in seven categories, similar to the HAPO study. The main outcomes were development of gestational diabetes mellitus (GDM), large-for-gestational-age (LGA) neonates and/or macrosomia, and primary cesarean section. Multivariate logistic regression analysis was used; significance was <0.05. RESULTS - A total of 6,129 women had a fasting glucose test at median of 9.5 weeks. There were strong, graded associations between fasting glucose level and primary outcomes. The frequency of GDM development increased from 1.0% in the lowest glucose category to 11.7% in the highest (adjusted odds ratio 11.92 [95% CI 5.39-26.37]). The frequency of LGA neonates and/or macrosomia increased from 7.9 to 19.4% (2.82 [1.67-4.76]). Primary cesarean section rate increased from 12.7 to 20.0% (1.94 [1.11-3.41]). CONCLUSIONS - Higher first-trimester fasting glucose levels, within what is currently considered a nondiabetic range, increase the risk of adverse pregnancy outcomes. Early detection and treatment of women at high risk for these complications might improve pregnancy Outcome.