Smoking or exposure to others’ tobacco smoke early in pregnancy may increase risk for certain congenital heart anomalies including septal defects, according to a presentation at the annual meeting of the American Heart Association.

“The heart’s basic structures develop very early in pregnancy, before many women realize they are pregnant,” said Sadia Malik, MBBS, MPH, the study’s lead author and an assistant professor of pediatrics at the University of Arkansas for Medical Sciences in Little Rock, AR. “Thus, even if a woman quits smoking at six weeks or later, her fetus will still have been exposed to the harmful effects of cigarette smoking during cardiac development.”

About 36,000 infants are born with a heart defect each year in the USA, according to the American Heart Association.

“From animal studies, we know that multiple components within cigarettes are harmful to the developing fetus and can cause mutations that might lead to birth defects,” Malik said.

In the population-based, case-controlled study, researchers investigated the association between congenital heart defects and maternal smoking. Collaborating with the National Birth Defects Prevention Study (NBDPS), researchers studied 566 infants with a congenital heart defect and 491 infants without one, as well as all parents.

Defects identified among the children included left-sided or right-sided obstructive defects that can restrict blood flow through the aortic valve or the pulmonary valve; septal heart defects; and conotruncal heart defects.

Mothers of infants from both groups were asked whether they smoked from one month before pregnancy through the end of pregnancy. Women’s exposure to tobacco smoke at home or work during the same period also was determined.

In the heart defect group, 34 percent of women reported they smoked some times in the month prior to conception through the end of the first trimester. This group was 60 percent more likely to have an affected infant than women who said they had not smoked, a correlation that remained after controlling for age, race, use of prenatal vitamins and limitation of alcohol intake.

Subgroup analysis estimated that women who had an infant with a septal or right-sided obstructive heart defect were 80 percent more likely to have smoked during embryo development than women who had an infant without a heart defect.

Malik suggested that some biological mechanisms such as apoptosis may play more of a role during septal and pulmonary valve development than during development of other cardiac structures.

“We hope our study contributes to the existing knowledge of the harmful effects of maternal smoking and tobacco smoke exposure on the developing infant,” Malik said. “We want to help develop a comprehensive approach to pre-conception clinical and public health interventions that will ultimately optimize the health of future generations.”

Malik noted the study is limited because maternal tobacco exposure was self-reported after pregnancy and the study focused on a small number of patients. Further study with a larger sample is needed to investigate the full impact of maternal smoking on the developing heart.