Obstetrical complications and physical aggression behaviours before the age of 2

To determine if infants who experienced obstetrical complications (OCs) have a greater tendency to show frequent physical aggression behaviours before the age of 2, independent of gender and family income. Another objective was to explain, at least partly, the sexual differences found in some behaviours using OCs. Data were from the Québec Longitudinal Study of Child Development (QLSCD). OCs were measured with Agpar scores (< 7) at 1 minute following birth. Family income level—sufficient or not—was measured when infants were about 5 months old. Twelve behaviours of physical aggression, opposition defiance, and hyperactivity were measured when infants were about 17 months old. Weighted data were analyzed using hierarchical log-linear models. Results suggest that infants with an Agpar score of less than 7 after birth are generally more likely to frequently display aggressive behaviours at 17 months, independent of gender and family income. Further, these results suggest it may be possible to explain, by OCs, the greater tendency in boys to frequently display aggressive behaviours at 17 months. Contrary to some hypotheses, it turns out that OCs have an impact on aggressive behaviours before the age of 2 independent of socioeconomic status.