Women who smoke during pregnancy can cause permanent vascular damage in their children -- increasing their risk for stroke and heart attack, researchers said today at the American Heart Association's 47th Annual Conference on Cardiovascular Disease Epidemiology and Prevention.
The Netherlands Atherosclerosis Risk in Young Adults (ARYA) study showed that participants who were exposed to smoke when their mothers were pregnant resulted in permanent cardiovascular damage that could be detected in young adulthood.
"This is the first report to demonstrate this association," said Cuno S. Uiterwaal, M.D., Ph.D., lead researcher and associate professor of clinical epidemiology at the University Medical Center Utrecht in The Netherlands. "This is a preventable risk factor. Women need to stop smoking, especially in pregnancy, not only for their own health, but for their unborn child."
Smoking during pregnancy can result in intrauterine growth retardation and low birth weight. Active and passive smoking in young adults also is associated with cardiovascular disease. But until the Dutch study, researchers were unsure whether this is due to a cumulative effect of smoke or whether children are vulnerable at specific periods, such as during gestation.
The study's 732 participants were born in 1970-73 and vascular risk measurements were performed in 1999-2000. Uiterwaal and colleagues found that adult offspring of the 215 mothers who smoked during pregnancy had thicker walls of the carotid arteries in the neck. The carotid artery intima-media thickness (CIMT), an ultrasound measurement of the thickness of the inner walls of the neck arteries, is used to determine the level of atherosclerosis. Offspring whose pregnant mothers were exposed to smoke had 13.4 micrometers thicker CIMT by young adulthood when compared to the offspring of mothers who did not smoke in pregnancy, researchers reported.
Even after the researchers adjusted for other risk factors in the young adults such as age, gender, body mass index, pulse pressure and cholesterol levels, the CIMT remained 9.4 micrometers thicker in children of mothers who smoked. Adjustment for current smoking by both mothers and fathers or the number of pack years (one "pack year" is 20 cigarettes smoked/day for one year) smoked by study participants also did not change this association.
"While it is difficult to separate the problem of current smoking and smoking during pregnancy, this study indicates that smoking in pregnancy has an independent effect," Uiterwaal said.
If both parents smoked during pregnancy, the children as young adults had thicker CIMT than other participants with either one smoking parent or parents who didn't smoke. Offspring of mothers who smoked the highest number of cigarettes during pregnancy had thicker CIMT than those born to mothers smoking less than the average or those who did not smoke.
"Our findings suggest that both smoking by mothers themselves in pregnancy and exposure to passive smoking are important," he said. "More exposure leads to more vascular damage in the offspring."
The researchers found that pregnancy was a critical period for damage from smoke exposure. They compared the children of mothers who didn't smoke during pregnancy and were currently not smoking to the children of mothers who didn't smoke in pregnancy but smoked now. They found no difference in CIMT. However, children from mothers who smoked in pregnancy, but who didn't currently smoke had significantly thicker CIMT compared to offspring of abstaining mothers. "There is the possibility that the compounds in tobacco smoke go through the placenta and directly damage the cardiovascular system of the fetus," Uiterwaal said. "The damage appears to be permanent and stays with the children."
When study participants were born, about 30 percent of the mothers smoked during pregnancy. But the current rate has dropped to between 5 percent and 7 percent due to health warnings, Uiterwaal said.
"There are still substantial numbers of mothers who smoke during pregnancy," he said. "This is just another reason for expectant mothers not to smoke." This is the first study in which researchers have dealt with this issue. Uiterwaal said further evidence should come from additional studies that show similar results.
Michiel L. Bots, M.D., Ph.D., second author of the study and associate professor of clinical epidemiology at the University Medical Center Utrecht in The Netherlands, presented the findings at the American Heart Association meeting.
The study's other co-author is Diederick E. Grobbee, M.D., Ph.D.
The ARYA study was funded by The Netherlands Organization of Health Research and Development Council.
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