That news appears in the April edition of Pediatrics.
Congenital heart defects are the most common type of structural birth defects, affecting eight to 10 of every 1,000 babies born in the U.S., according to the researchers, who included Sadia Malik, MD, MPH, of the University of Arkansas.
Malik's team studied interviews of 7,000 women who had babies between 1997 and 2002. The group included nearly 3,100 mothers of babies born with congenital heart defects. The other mothers had babies with no heart defects or other birth defects.
The women were asked about their smoking habits during a four-month period, starting the month before pregnancy and ending after the first three months of pregnancy; 19% reported smoking during that time.
Compared to mothers of healthy babies, mothers of babies with septal heart defects (a hole between the heart's right and left chambers) were 44% more likely to report light smoking (up to 14 cigarettes a day), 50% more likely to report moderate smoking (15-24 daily cigarettes), and twice as likely to report heavy smoking (at least 25 daily cigarettes).
By the same comparison, heavy smoking was also more often reported by mothers of babies with right-sided obstructive defects, which make it hard for blood to flow from the heart's right side.
Secondhand smoke wasn't linked to congenital heart defects.
The findings held when the researchers considered factors including the mothers' age and race. But Malik and colleagues note that they may have overlooked other risks. The researchers also can't confirm that the mothers accurately recalled their smoking habits around the time of pregnancy.
The study doesn't prove that smoking causes congenital heart defects. But a CDC news release about the study points out that smoking can make it harder to get pregnant and have a healthy pregnancy and a healthy baby.
"Most people know that smoking causes cancer, heart disease, and other major health problems," Margaret Honein, PhD, MPH, of the CDC's National Center for Birth Defects and Developmental Disabilities, says in a news release. "The indisputable fact is that women who smoke during pregnancy put themselves and their unborn babies at risk for other health problems."