Smoking during pregnancy lowers not only birthweight but IQ

July 1, 2005

Women who smoke cigarettes during their third trimester give birth to boys with IQs up to 6.2 points lower than boys born to non-smoking counterparts, according to a recent Danish study.

Women who smoke cigarettes during their third trimester give birth to boys with IQs up to 6.2 points lower than boys born to non-smoking counterparts, according to a recent Danish study.

The study included approximately 3,000 males with a mean age of 18.7 years. Their mothers were placed in one of five categories based on their smoking habits during their third trimester: (1) Nonsmoking; (2) <3 cigarettes daily; (3) 3–10 cigarettes daily; (4) 11–20 cigarettes daily; or (5) >20 cigarettes daily.

The results revealed a clear dose-response relationship between maternal smoking and offspring IQ and between maternal smoking and birthweight and birth length. The more cigarettes the mothers smoked per day, the less their male offspring weighed and measured at birth and the lower the males scored on intelligence tests as adults. The results suggest that smoking during pregnancy may have serious long-term consequences on intellectual as well as physical development.