Aim: To investigate whether breastfeeding during infancy is a determinant of intelligence at 3.5 y. Methods: Five hundred and fifty European children enrolled at birth in the Auckland Birthweight Collaborative Study were assessed at 3.5 y of age. Approximately half were small for gestational age (SGA10th percentile) at birth and half were appropriate for gestational age (AGA>10th percentile). Duration of breastfeeding was recorded at maternal interview, and the intelligence of children was assessed using the Stanford Binet Intelligence Scale. Regression analysis was used to calculate estimates of difference in intelligence scores between breastfeeding groups for the total sample and the group of SGA children. Analyses of the total sample were weighted to account for the disproportionate sampling of SGA children. Results: Breastfeeding was not significantly related to intelligence scores in the total sample despite a trend for longer periods of breastfeeding to be associated with higher intelligence scores. However, in the SGA group, breastfeeding was significantly related to IQ at 3.5 y. Small for gestational age children who were breastfed for longer than 12 mo had adjusted scores 6.0 points higher than those who were not breastfed (p=0.06).
Conclusion: Breastfeeding may be particularly important for the cognitive development of preschool children born small for gestational age.