Mothers who smoke during the first trimester of pregnancy are more likely to give birth to babies with some of the most common types of birth defects, a new study finds.
Specifically, women who smoked early in pregnancy were 30 percent more likely to give birth to babies with obstructions in the flow of blood from the heart to the lungs, and nearly 40 percent more likely to have babies with openings in the upper chambers of their hearts.
"For women who are planning to become pregnant, if they are smokers, they should stop smoking," study author Dr. Adolfo Correa of the Centers for Disease Control and Prevention (CDC) told Reuters Health. And if they find out they are pregnant, "they should stop smoking right away."
These findings add to previous evidence that suggested smoking may increase the risk of some congenital heart defects, the most common type of birth defects.
To investigate further, Correa and his team reviewed information collected from mothers of 2,525 infants with congenital heart defects and mothers of 3,435 similar infants who were born with healthy hearts.
Correa and his team focused on two types of heart defects already linked to smoking in pregnancy - obstructions in blood flow from the right side of the heart to the lungs and openings between the upper chambers of the heart.
These abnormal openings in the heart's upper chambers occur in roughly one out of every 1,000 babies in the general population, Correa noted. The obstructions in blood flow to the lungs are slightly less common, occurring at a rate of 0.6 per 1,000 babies in the U.S., he said.
Based on his results, if moms choose to smoke during pregnancy, those rates increase - women who smoked during early pregnancy were 36 percent more likely to have a baby with these abnormal openings, and 32 percent more likely to have a baby born with this type of obstruction in blood flow to the lungs.
The findings appear in the journal Pediatrics.
Smoking in the second and third trimesters may also pose risks to the unborn baby, Correa noted, but he and his colleagues focused on the first trimester because this is the time when most organs are being developed, and the fetus is "most susceptible to the effects of environmental conditions." But this is also the time when women are least likely to know they are pregnant, making it even more imperative they stop smoking before any chance of pregnancy occurs, he added.
It's not clear how smoking may affect heart development, Correa noted - it might somehow lower levels of folate, known to prevent birth defects. "We don't really know the mechanism for how smoking might be associated with heart defects," he said.
Heart problems aren't the only risk to babies associated with smoking in pregnancy, he said - moms who maintain the unhealthy habit are also more likely to have pre-term or very small babies and to have babies born with cleft lip and palate.
Overall, 40,000 babies are born with some type of congenital heart defect every year, according to the CDC.
A news release from the CDC adds that this study and other research suggest that if women quit smoking before or very early in pregnancy, they could avoid as many as 100 cases of the obstruction type of heart defect and 700 cases of abnormal openings in the upper heart chambers each year in the United States.