Please cite this paper as: Falgreen Eriksen H, Mortensen E, Kilburn T, Underbjerg M, Bertrand J, Støvring H, Wimberley T, Grove J, Kesmodel U. The effects of low to moderate prenatal alcohol exposure in early pregnancy on IQ in 5-year-old children. BJOG 2012;119:1191-1200. Objective To examine the effects of low to moderate maternal alcohol consumption during early pregnancy on children's intelligence (IQ) at age 5 years. Design Prospective follow-up study. Setting Neuropsychological testing in four Danish cities 2003-2008. Population A cohort of 1628 women and their children sampled from the Danish National Birth Cohort. Methods Participants were sampled based on maternal alcohol consumption during pregnancy. At 5 years of age, children were tested with the Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R). Parental education, maternal IQ, maternal smoking in pregnancy, the child's age at testing, gender, and tester were considered core confounding factors, whereas the full model also controlled for maternal binge drinking, age, BMI, parity, home environment, postnatal smoking in the home, health status, and indicators for hearing and vision impairments. Main outcome measures The WPPSI-R. Results No differences in test performance were observed between children whose mothers reported consuming between one and four or between five and eight drinks per week at some point during pregnancy, compared with children of mothers who abstained. For women who reported consuming nine or more drinks per week no differences were observed for mean differences; however, the risks of low full-scale IQ (OR 4.6; 95% CI 1.2-18.2) and low verbal IQ (OR 5.9; 95% CI 1.4-24.9) scores, but not low performance IQ score, were increased. Conclusions Maternal consumption of low to moderate quantities of alcohol during pregnancy was not associated with the mean IQ score of preschool children. Despite these findings, acceptable levels of alcohol use during pregnancy have not yet been established, and conservative advice for women continues to be to avoid alcohol use during pregnancy.