March 7, 2011 -- Pregnant women who don’t smoke but breathe the secondhand smoke of others have an increased risk for delivering stillborn babies or babies with birth defects, according to a new research review.
Secondhand smoke exposure has been linked to lower birth weight, but it has not been clear if exposure during pregnancy influences other birth outcomes in nonsmoking women.
In an effort to better understand the relationship, researchers from the University of Nottingham in the U.K. analyzed 19 studies that examined birth outcomes among nonsmoking women exposed to tobacco smoke during pregnancy.
The data showed a 23% increase in the risk of stillbirth associated with passive smoke exposure and a 13% increase in the risk of birth defects.
The analysis, which appears in the April issue of Pediatrics, failed to show a relationship between secondhand smoke exposure and miscarriage before 20 weeks of gestation or death around the time of birth.
“I think we can confidently say from this analysis that secondhand smoke exposure during pregnancy increases the risk for stillbirth and delivering a baby with congenital malformations,” says study researcher Jo Leonardi-Bee, PhD, of the U.K. Center for Tobacco Control Studies at the University of Nottingham. “These findings confirm the importance of avoiding such exposures, both in the home and in public places.”
Secondhand Smoke in the Home
By one estimate, 126 million nonsmokers in the U.S. are regularly exposed to secondhand smoke.
Leonardi-Bee says the home remains the biggest source of secondhand smoke exposure for most nonsmoking women.
“Smoking bans have certainly reduced exposures in public places and in work settings, but, of course, they don’t address the problem of home exposure,” she says.
Pediatrician Jonathan P. Winickoff, MD, of Harvard Medical School, researches the effects of secondhand cigarette smoke exposure on babies and children. He tells WebMD that smoking during pregnancy is the No. 1 preventable cause of low birth weight and neonatal intensive care (NICU) admissions.
“Roughly one in five NICU babies are there because of smoke exposure,” he says. “The study illustrates that secondhand smoke exposure is a cause for concern, just like primary smoke exposure.”
Pediatrician Dana Best, MD, who directs the Smoke Free Project at the Children’s National Medical Center in Washington, D.C., points to studies suggesting that workplace and public smoking bans have had the unintended consequence of increasing smoke exposures inside the home.
“As smokers find fewer and fewer public places to smoke, they may be smoking more at home,” she tells WebMD.
Winickoff adds that tobacco companies spend billions of dollars each year promoting their products, and those dollars are mostly aimed at young adults.
“Young women are much more likely than other women to both take up smoking and become pregnant,” he says. “It is a dangerous intersection.”