Do children born to teenage parents have lower adult intelligence? A prospective birth cohort study

Teenage motherhood has been associated with a wide variety of negative offspring outcomes including poorer cognitive development. In the context of limitations of previous research, this paper assesses the contemporary relevance of this finding. In this study we investigate the long-term cognitive status (IQ) among 21 year adult offspring born to teenage parents using the Mater University Study of Pregnancy- a prospective birth cohort study, which recruited all pregnant mothers attending a large obstetrical hospital in Brisbane, Australia, from 1981 to 1983. The analyses were restricted to a sub-sample of 2643 mother-offspring pair. Offspring IQ was measured using the Peabody Picture Vocabulary Test at 21 year. Parental age was reported at first clinic visit. Offspring born to teenage mothers (<20 years) have -3.0 (95% Confidence Interval (CI): -4.3, -1.8) points lower IQ compared to children born to mothers ≥20 years and were more likely to have a low IQ (Odds Ratio (OR) 1.7; 95% CI: 1.3, 2.3). Adjustment for a range of confounding and mediating factors including parental socioeconomic status, maternal IQ, maternal smoking and binge drinking in pregnancy, birthweight, breastfeeding and parenting style attenuates the association, though the effect remains statistically significant (-1.4 IQ points; 95% CI: -2.8,-0.1). Similarly the risk of offspring having low IQ remained marginally significantly higher in those born to teenage mothers (OR 1.3; 95% CI: 1.0, 1.9). In contrast, teenage fatherhood is not associated with adult offspring IQ, when adjusted for maternal age. Although the reduction in IQ is quantitatively small, it is indicative of neurodevelopmental disadvantage experienced by the young adult offspring of teenage mothers. Our results suggest that public policy initiatives should be targeted not only at delaying childbearing in the population but also at supporting early life condition of children born to teenage mothers to minimize the risk for disadvantageous outcomes of the next generation.