Prenatal exposure to tobacco: II. Effects on cognitive functioning at age three.

Three-year-old children, born to women who smoked ten or more cigarettes at the beginning of pregnancy and identified at the time of registration for prenatal care, were assessed by the McCarthy Scales of Children's Abilities and the Minnesota Child Development Inventory. Children whose mothers quit smoking during pregnancy relative to children whose mothers persisted in smoking performed at a statistically significant higher level on the General Cognitive Index of the McCarthy and on each of the three subscales from which the General Cognitive Index is derived. The scores on the Minnesota Child Development Inventory were similar in showing a higher performance in the children of quitters. Statistical adjustment for environmental factors, characteristics of the child, and fetal maturity did not account for the observed differences between children of women who quit smoking and those of women who continued to smoke.