LOS ANGELES—A new study provides additional evidence that in utero exposure to maternal smoking increases the risk of physician-diagnosed asthma and wheezing during childhood.[1] In addition, the study indicates that current exposure to environmental tobacco smoke (ETS) raises the risk that a child will experience wheezing and other symptoms of asthma. However, this does not increase the prevalence of physician-diagnosed asthma per se.

“Children exposed in utero to maternal smoke are at substantial risk of developing asthma,” Frank D. Gilliland, MD, told RESPIRATORY REVIEWS. “We really need to do a better job at smoking cessation and preventing initiation of smoking among women of childbearing age,” he said.

INDEPENDENT EFFECTS

Few studies have examined the independent effects of in utero exposure to active maternal smoking and postnatal ETS exposure. Dr. Gilliland and colleagues used data from the Children’s Health Study to investigate these independent effects in 5,762 school-age children living in Southern California. The Children’s Health Study is a 10-year longitudinal study of the effects of air pollution on children’s respiratory health. “I think our population is relatively unique. We studied a large multiethnic population from 12 communities,” said Dr. Gilliland.

“We paid particular attention to the effects of maternal smoking on asthma because it’s something that has really changed in the last two to three decades and may underlie a part of the increase in asthma that is occurring in kids in this country,” noted Dr. Gilliland, Associate Professor of Occupational and Environmental Health at the University of Southern California. “I think our focus on the relationship between in utero exposure and asthma onset is relatively unique. Most studies have been looking at the effects of environmental tobacco smoke on the severity of asthma,” he added.

In utero exposure to maternal smoking was defined as any smoking during pregnancy. ETS exposure was defined as any current or past household exposure to environmental tobacco smoke, including in utero exposure. The percentage of children exposed to maternal smoking in utero was 18.8%; 39.5% of the children had any lifetime exposure to ETS. The lifetime prevalence of wheezing was 33.7%. The percentage of children who had a diagnosis of asthma was 14.6%.

In utero exposure to maternal smoking was independently associated with an increased prevalence of physician-diagnosed asthma and wheezing. Further, it was independently associated with all of the subcategories of asthma and wheezing that were assessed, including asthma with current symptoms, asthma requiring medication use in the previous 12 months, lifetime history of wheezing, and emergency room visits during the previous year. The effects of in utero exposure to maternal smoking did not differ significantly between the sexes.

In contrast, neither current nor past ETS exposure was associated with increased asthma prevalence. However, “ETS was associated strongly with wheezing and some of the symptomatic outcomes, consistent with other studies,” Dr. Gilliland said.

To better understand the relationship between maternal smoking and asthma, Gilliland et al are conducting a nested, case-control study to determine the effects of dose and duration of tobacco use during pregnancy on asthma development. They are also studying genetic factors associated with tobacco metabolism to see whether they modify the risk of maternal smoking.

—Deborah L. O’Connor

Reference
1. Gilliland FD, Li Y-F, Peters JM. Effects of maternal smoking during pregnancy and environmental tobacco smoke on asthma and wheezing in children. Am J Respir Crit Care Med. 2001;163:429-436.