Introduction Preterm births have been associated with behavioural problems later on. This study aimed to investigate whether late preterm (LPT) children (34–36 weeks gestation) are at increased risk of presenting behavioural problems at the age of 4 years old comparatively to full term children (37–42 weeks).

Methods Children from the 2004 Pelotas Birth Cohort were enrolled just after birth and were followed-up at home in several occasions when information on a series of maternal (socio-economic, demographic, reproductive, and behavioural characteristics, and maternal depression) and child co-variables (intensive care unit hospitalisation at birth, hospitalisations during the first year, breastfeeding duration and bed-sharing) was collected by trained fieldworkers. Estimated gestational age was based on last menstrual period or, when unknown or inconsistent, through the Dubowitz method. Presence of behavioural problems was assessed through application of the Child Behaviour Checklist (CBCL) to the mothers. Adjusted analyses were run through linear regression.

Results There were 4231 livebirths, 14.5% were preterm newborns, 77% of whom were LPT. A total of 3411 children were assessed at the age of 4 years (416 LPT and 2995 full term). Mean CBCL rates were higher for LPT than for full term children (36.6 and 34.2, respectively; p=0.007). After allowing for confounders (family income, maternal and child characteristics) the association was no longer significant (β=0.4; SE=0.9; p=0.635). No interaction was observed between LPT and any of the studied co-variables.

Conclusion LPT children present higher rates in CBCL than term children, but the difference relies mainly on lower socioeconomic conditions.