Mental development of children whose mothers smoked during pregnancy.

The relationship between maternal smoking during pregnancy other parental and neonatal factors and childrens subsequent cognitive development was analyzed in data from the Collaborative Perinatal Study. The children of mothers who had smoked during pregnancy had slightly lower scores (3-4%) on spelling and reading tests at 7 years of age had more frequent short attention spans and were more often hyperactive than the children of nonsmokers. Arithmetic scores were not significantly different. Comparison of siblings whose mothers smoked in only 1 of their 2 pregnancies revealed that childrens achievement test scores were 2-5% lower and behavioral abnormalities were 2% more frequent when the mothers had smoked. Neonates hemoglobin levels increased with the number of cigarettes mothers smoked during pregnancy. Offspring of the heaviest smokers who had short attention spans or were hyperactive had significantly higher hemoglobin values as neonates than children with normal attention spans and activity levels. The correlation between high hemoglobin levels and abnormal behavior was not found in the children of nonsmokers. Finally smokers children who had short attention spans had lower birthweights than children who subsequently showed normal attention spans a correlation that was not present in the children of nonsmokers. These findings strengthen the hypothesis that cognitive and behavioral abnormalities are caused by maternal smoking. These abnormalities may be a result of smoking-induced fetal hypoxemia. At present medical practice is unable to eliminate the influence of smoking-associated fetal growth retardation or increased neonatal hemoglobin levels.