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CHICAGO -- Babies exposed to tobacco smoke in the first gestational trimester are at an elevated risk of congenital heart disease, researchers said here.
CHICAGO, Nov. 15 -- Tobacco smoke exposure early during pregnancy may impair formation of the baby's heart, researchers said here.
Infants of women who smoked during the first trimester were 60% more likely to have congenital heart disease, said Sadia Malik, M.B.B.S, M.P.H., of the University of Arkansas in Little Rock, and colleagues, at the American Heart Association meeting.
Although smoking has been known to cause a variety of pregnancy complications, this finding adds to the evidence of cardiovascular harm and may be useful when counseling patients on smoking cessation, commented Gerald Fletcher, M.D., of the Mayo Clinic in Jacksonville, Fla., who was uninvolved in the study.
Dr. Malik said it should send a strong message to patients. "If you are planning a pregnancy you should stop smoking," she said. "All women of reproductive age who could potentially get pregnant should stop smoking."
The population-based study in Arkansas included 566 infants with nonsyndromic heart defects and 491 without, and their parents, as part of a larger 10-state birth defects surveillance program. Mothers were interviewed by phone about smoking behaviors and secondhand smoke exposure at home and work during the period from the month prior to pregnancy through the end of the first trimester.
The researchers found that women who had infants with heart defects were more likely to have smoked during the month before pregnancy to the end of the first trimester than women who had infants without birth defects (34% versus 25%, odds ratio 1.6, 95% CI 1.2 to 2.1).
This relationship persisted after adjustment for confounding factors prenatal vitamin use, alcohol intake, maternal age, and race or ethnicity.
The findings of a subgroup analysis were:
Most of the women averaged half a pack of cigarettes a day. Infants born with a heart defect were more likely to be premature and have lower birth weight than controls.
In the heart defect group, secondhand smoke exposure at work or home was significantly more common during the first trimester of pregnancy and the month prior to pregnancy than among controls (OR 1.3, 95% CI 1.01 to 1.7).
"We did not find that if a mother smoked heavily there was an increased risk of severe heart defects," Dr. Malik reported.
However, she cautioned that most mothers don't realize how much smoke they are exposed to and may have underreported it.
About 36,000 babies each year are born with heart defects, which is an incidence of eight to 10 per 1,000 births, Dr. Malik said. If all women were to stop smoking, about 2,000 per year could be prevented, she estimated.
Most of the causes of heart defects are unknown, but the researchers said they are likely a combination of genetic and environmental factors. The mechanism through which smoking works could be apoptosis, Dr. Malik speculated.
"The congenital heart defects don't contribute a lot to childhood mortality but they do contribute a lot of morbidity," she said, and while such defects can typically be treated, "the easiest way is to prevent it."
The researchers acknowledged the study's small sample size and said that the larger surveillance program may provide more definitive data.