Maternal age and cognitive and behavioural outcomes in middle childhood.

The relationships between maternal age and childhood cognitive and behavioural outcomes were analysed in a birth cohort of New Zealand children studied until the age of 13 years. Increasing maternal age was associated with increasing scores on tests of cognitive ability and achievement and with decreasing reports of conduct problems. The correlations between maternal age and childhood cognitive/behavioural outcomes ranged from 0.11 to 0.21 with a median value of 0.18. These associations were adjusted statistically for the effects of maternal social background at the time of birth and for childhood history subsequent to birth. This analysis suggested that the poorer outcomes for children born to younger mothers reflected the cumulative effects of two sets of factors which placed these children at a disadvantage. Firstly, the offspring of younger mothers tended to be born into relatively poorly educated, socially disadvantaged families and secondly, these children were exposed to less nurturant and more changeable home environments. The net effects of differences in social background at birth and childrearing environments subsequent to birth were sufficient to explain most of the apparent correlation between maternal age and childhood cognitive/behavioural outcomes.