Smoking cigarettes during pregnancy may not only increase the risk of problems during and after pregnancy for the mother, but a new report shows that tobacco smoke may actually cause genetic damage to the developing fetus, which could increase the risk of cancer as a child and adult.

It’s the first report to document genetic damage in fetal cells from women who smoked before and during pregnancy. Previous studies showed the possibility of DNA damage caused by smoking during pregnancy, but used only indirect evidence.

Researchers compared the number of genetic abnormalities in fetal cells taken from the amniotic fluid (liquid that surrounds the fetus) of women who smoked while pregnant and compared them with cells taken from nonsmoking pregnant women. The results showed that there were 3.5 times as many structural genetic abnormalities in the fetal cells taken from smokers vs. nonsmokers.

The findings appear in the March 9 issue of The Journal of the American Medical Association.

“Such results, if substantiated, would provide direct evidence of tobacco-associated intrauterine [genetic mutations] and could have important implications for the immediate and long-term health effects of children born to mothers who smoke,” write David M. DeMarnini, PhD, and R. Julian Preston, PhD, of the Environmental Protection Agency, in an editorial that accompanies the study.

Cigarette Smoke Linked to Genetic Damage

In the study, researchers looked at whether smoking before and during pregnancy by women has a genetically toxic effect on fetal cells.

Researchers compared the level of chromosomal instability, a measure of genetic damage, in fetal cells taken from the amniotic fluid of 25 smokers and 25 nonsmokers. All of the smokers had smoked 10 or more cigarettes per day for 10 years or more and continued to smoke during pregnancy.

In comparing the genetic data between the smokers and nonsmokers, researchers found a number of important differences in the proportion of genetic abnormalities. For example, 12.1 percent of the fetal cells taken from the smoking mothers had evidence of structural genetic abnormalities compared with 3.5 percent of the others.

Fetal cells from smoking mothers also had a higher proportion of genetic instability and chromosomal lesions.

Researchers say a certain chromosomal region was most affected by tobacco smoke, and this area has been implicated in the development of blood cancers, which may explain the link between smoking during pregnancy and childhood leukemia reported by previous studies.

They say more studies will be needed to determine whether the children of smokers have a higher risk of developing cancer in their lifetimes.

“In the meantime, the message to women based on the published literature remains clear: Smoking during pregnancy can be hazardous for both the fetus and the mother,” write the editorialists.

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: de la Chica, R. The Journal of the American Medical Association, March 9, 2005; vol 293: pp 1212-1222.