Duration of gestation, size at birth and later childhood behaviour.

Although many previous studies have reported an association between preterm birth or small size at birth and later behaviour, multiple methodological limitations threaten the validity of causal inferences from reported associations. The authors have examined the association between gestational age and gestational age-specific size at birth (weight, length and head circumference) and behaviour in a large sample of children born healthy at term. The data were from the 6.5-year follow-up of 13,889 Belarusian children who participated in the Promotion of Breastfeeding Intervention Trial, a cluster-randomised trial of a breast-feeding promotion intervention. Child behaviour was measured using the parent and teacher versions of the Strengths and Difficulties Questionnaire (SDQ). Differences in SDQ scores by gestational age and by birthweight, birth length and birth head circumference standardised for gestational age and sex (z-scores) were analysed after controlling for potentially confounding maternal and family factors. There was no association between gestational age and child behaviour after adjusting for potential confounding factors. Lower birthweight-for-gestational age was associated with higher scores in problem behaviours including total difficulties, conduct problems, hyperactivity, emotional symptoms and peer problems. Similar but smaller differences were observed with birth length and birth head circumference, but those differences were attenuated with adjustment for birthweight. The patterns of association were consistent in both parent and teacher assessments. Among school-age children born at term within normal range of birthweight, fetal growth, but not gestational age, was associated with behavioural problem scores.