Spanish researchers have discovered the first direct evidence that smoking by pregnant women can damage the genes of their unborn fetuses. They say that some of the genetic mutations they observed raise the newborn's risk of developing leukemia.
In a study of 50 pregnant women, scientists in Barcelona found more abnormalities in fetal cells taken from the 25 women who smoked than in the other 25 who had never used tobacco.
The abnormalities occurred in fetal chromosomes, the microscopic strings of DNA in cells that contain genes. Such aberrations can lead to disease and other dysfunction. The Spanish researchers saw the abnormalities after extracting cells the fetuses shed into the fluid surrounding them in the womb.
In a report in the Journal of the American Medical Association, they say the smoking mothers had about three times more fetal genetic alterations than the non-smoking women.
Physician Josep Egozcue of the Autonomous University of Barcelona says his team found that one particular fetal chromosome region was the most frequently disturbed.
"Chromosome instability is known to be linked to cancer," said Josep Egozcue. "But we found abnormalities in a specific chromosome region which are present in many types of leukemia, especially in infants with leukemia, but also in children and adults."
Scientists have never before found such direct genetic evidence of the toxicity of maternal smoking on a developing fetus.
The study was rigorous. The researchers set rigid conditions that limited the number of participants to fifty. None could have been exposed to other potential gene-altering agents during their pregnancy, such as radiation, alcohol, or caffeine. The smokers had to have had at least 10 cigarettes a day for 10 years, while the non-smokers could not have been exposed to the exhaled smoke of others anywhere while pregnant.
A U.S. government scientist who studies cancer-causing agents in the environment, David DeMarini, calls the study heroic.
"That's one reason this study has never been done before," said David DeMarini. "No one has ever gone out and said, 'Let's find some smoking mothers and non-smoking mothers and look at the actual cells of the baby for chromosomal mutations.'"
However, Mr. DeMarini argues that the study is not definitive because of its small size and some other reasons. His major criticism is that the chromosome mutations detected are the very same kind that occur spontaneously in the laboratory when cells are cultured and grown for several days in a dish, as were the studied fetal cells. But he is not discounting the findings completely.
"The fact is there are three times more of them, mutations, showing up in the smokers than in the non-smokers, so you can't completely ignore it," he said.
Dr. Egozcue in Barcelona says that is precisely the point of the study. He questions Mr. DeMarini's argument.
"They say that [lab] culture conditions may have influenced the results, but all cultures were subject to the same conditions," he said. "So why did these conditions, then, affect the smokers' fetuses more than the other ones? I don't understand."
David DeMarini says that, although the study should be repeated with larger numbers of participants, it does conform to what is already known about the hazards of smoking during pregnancy, and that pregnant women should take note.