Smoking During Pregnancy Increases Wheeze and Asthma Risk in Preschool Children

Maternal smoking during pregnancy is associated with wheeze and asthma in preschool children, even among children who were not exposed to maternal smoking late in pregnancy or after birth, according to a new study published in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine.

"Epidemiological evidence suggests that exposure to maternal smoking during fetal and early life increases the risk of childhood wheezing and asthma, but earlier studies were not able to differentiate the effects of prenatal and postnatal exposure," said Åsa Neuman. MD, lead author from the Institute of Environmental Medicine at the Karolinska Institutet in Stockholm, Sweden.

The study, a large pooled analysis of eight European birth cohorts, included a total of 21,600 children, of which 735 were exposed to maternal smoking only during pregnancy. Exposure information and information on symptoms of wheeze and asthma were derived from parental questionnaires.

In analyses adjusted for sex, parental education, parental asthma, birth weight, and siblings, maternal smoking only during pregnancy was associated with increased risks for wheeze (odd ratio 1.39, 95% CI 1.08-1.77) and asthma (odds ratio 1.65, 1.18-2.31) at age 4 to 6 years. Moreover, maternal smoking during the first trimester of pregnancy, but not during the third trimester or the first year following birth, was associated with increased risks for subsequent wheeze and asthma.

"These results indicate that the harmful effects of maternal smoking on the fetal respiratory system begin early in pregnancy, perhaps before the women is even aware that she is pregnant," said Neuman.

The study’s authors do point out that the study has some limitations, including the use of parental questionnaires to obtain exposure and outcome information.

"Our large pooled analysis confirms that maternal smoking during pregnancy, particularly during the first trimester, is associated with a greater risk of offspring developing wheeze and asthma when they reach preschool age," concluded Neuman. "Teens and young women should be encouraged to quit smoking before getting pregnant."

Source: American Thoracic Society