Kids born to older mothers are smarter: Study

There's good news for career women. Overturning conventional wisdom, a new study suggests that delaying pregnancy till age 35 can actually make your kids smarter.

In contrast to 40 years ago, children born to older mothers today are more likely to perform better in cognitive ability tests than those born to younger mothers, said the study published in the International Journal of Epidemiology

"Our research is the first to look at how the cognitive abilities of children born to older mothers have changed over time and what might be responsible for this shift," said study lead author Alice Goisis, researcher at london School of Economics and Political Science.

This shift is due to the changing characteristics of women who have children at an older age, the study said.

Older mothers today tend to be more advantaged than younger mothers -- for example, they are well educated, are less likely to smoke during pregnancy and are established in professional occupations. This was not necessarily true in the past.

For the study, the researchers analysed data from three longitudinal studies in Britain -- the 1958 National Child Development Study, the 1970 British Cohort Study and the 2001 Millennium Cohort Study. 

Children's cognitive ability was tested when they were 10/11 years old.

In the 1958 and 1970 cohorts children born to mothers aged 25-29 scored higher than children born to mothers aged 35-39. 

In the 2001 cohort, this result was reversed. 

When the researchers took the mothers' social and economic characteristics into account, the differences across cohorts disappeared. 

This indicates that the changing characteristics of women who have children at an older age were highly likely to be the reason for the differences.

"Cognitive ability is important in and of itself but also because it is a strong predictor of how children fare in later life -- in terms of their educational attainment, their occupation and their health," Goisis said.