Smoking during pregnancy and its effects on child cognitive ability from the ages of 8 to 12 years.

Maternal smoking during pregnancy and subsequent child cognitive development and ability were examined in a birth cohort of New Zealand children studied to the age of 12 years. Analysis at a bivariate level showed that children whose mothers smoked during pregnancy scored significantly lower on standardised tests of intelligence, reading and mathematical ability than children whose mothers did not smoke. However, after adjustment for confounding covariates, the results showed no detectable relationship between smoking during pregnancy and child cognitive ability. These results suggest that children whose mothers smoked during pregnancy fared worse on tests of cognitive ability not because of possible causal effects of smoking, but rather because these children tended to come from families which provided a relatively disadvantaged home environment.