Children whose mothers smoked during pregnancy may be at risk of becoming overweight by the age of 8, a large U.S. study has found.

The findings add to evidence that although prenatal smoking can cause low birth weight, it may raise the odds of excessive weight gain in childhood.

They also point to yet another reason for women to quit smoking before pregnancy, according to lead study author Dr. Aimin Chen, a researcher at the U.S. National Institute of Environmental Health Sciences.

Besides low birth weight, prenatal smoking has been shown to raise the risk of miscarriage, premature delivery and other pregnancy complications, Chen noted in an interview.

The current study, published in the International Journal of Epidemiology, is based on data from nearly 35,000 children who were born between 1959 and 1965 and followed through the age of 8. Mothers reported on their smoking habits during pregnancy, and the children had their weight and height measured at ages 1, 3, 4, 7 and 8.

Overall, children of smokers were more likely to be overweight or on the verge of becoming overweight by the age of 8. At that age, the risk of being overweight climbed about 17 percent for every 10 cigarettes a mother smoked per day while pregnant.

The connection between prenatal smoking and childhood weight remained when the researchers accounted for factors such as family income and the mother’s weight, race and education.

This is the largest study to date to look at this question, Chen told Reuters Health, and the results are in line with those of previous studies - including a UK study that linked prenatal smoking to a higher risk of obesity into adulthood.

The reason, according to Chen, may have to do with the fact that prenatal smoking often leads to low birth weight. Infants born at a low weight tend to go through a rapid period of “catch-up” growth, and this accelerated growth may make them more vulnerable to excess weight gain later in life.

It’s also possible, Chen and his colleagues write, that infants of smokers go through a form of nicotine withdrawal after birth, and - similar to smokers trying to kick the habit - develop problems with appetite control.

Whatever the reason for the link, Chen said the study gives women “one more reason” to avoid smoking.

SOURCE: International Journal of Epidemiology, February 2006.