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Despite considerable progress, there are still many pregnant women who are not fully aware of the significant risks that smoking poses to babies. But it’s not just mothers that need to stay away from smoking. According to a new study, fathers-to-be who smoke may place their offspring at an increased risk of congenital heart defects.

Smoking during pregnancy causes adverse health outcomes that can affect women and infants during and after pregnancy — such as placenta previa, placental abruption, miscarriage, preterm birth, and premature membrane rupture. Infants born to women who smoke are also at higher risk for low birthweight (LBW), stillbirth, infant death (sudden infant death syndrome, or SIDS). Smoking can also lead to conceptual delay and infertility in women of childbearing age. Despite these risks, according to US Pregnancy Risk Assessment Monitoring System, 23% of US women smoked in the 3 months before pregnancy and almost 11% smoked during the last trimester of pregnancy.

The reason why tobacco smoke is associated with so many harmful effects has to do with the high number of carcinogens — chemicals that cause cancer — that it contains. These carcinogens accumulate in the body causing damage to all organs, including the reproductive ones, but also the developing fetus. Because smoking alters the chemical environment of the smoker’s body, for instance by lowering oxygen supply, this can affect the outcome of a healthy pregnancy even before a woman conceives.

“Smoking is teratogenic, meaning it can cause developmental malformations. The association between prospective parents smoking and the risk of congenital heart defects has attracted more and more attention with the increasing number of smokers of childbearing age,” Dr. Jiabi Qin, from the Xiangya School of Public Health, Central South University in China, said in a statement.

Congenital heart defects are the leading cause of stillbirth, affecting 8 in 1,000 babies born worldwide. One of the leading causes of congenital heart defects is smoking during pregnancy.

While most studies have focused on women smokers, Qin and colleagues performed the first study that examined the relationship between paternal smoking and the risk of congenital heart defects in offspring. The researchers combed through 125 studies involving 137,574 babies born with congenital heart defects 8.8 million parents.

Strikingly, the risk of congenital heart defects was much greater in men who smoke than in woman smokers. According to the results of the meta-analysis, the associated risk of congenital heart defects increased by 74% for men smoking, 124% for passive smoking in women, and 25% for women smoking (all compared to no exposure). These risks are significant because maternal passive smoking and paternal smoking are more common than maternal active smoking. This may be due to the many pregnant women who are aware that they risk harming their babies if they smoke but place less emphasis on exposure to tobacco smoke in their environment.

“Women should stop smoking before trying to become pregnant to ensure they are smoke-free when they conceive,” said Dr. Qin. “Staying away from people who are smoking is also important. Employers can help by ensuring that workplaces are smoke-free.”

“Doctors and primary healthcare professionals need to do more to publicize and educate prospective parents about the potential hazards of smoking for their unborn child,” he added.

The findings appeared in the European Journal of Preventive Cardiology.