New research has discovered that mothers who smoke during pregnancy may cause wheeze and asthma in their children when they reach preschool, even among kids whose moms did not smoke until late pregnancy or after birth.

Asa Neuman, MD, of the Institute of Environmental Medicine at the Karolinska Institutet in Stockholm, Sweden, said:

“Epidemiological evidence suggests that exposure to maternal smoking during fetal and early life increases the risk off childhood wheezing and asthma, but earlier studies were not able to differentiate the effects of prenatal and postnatal exposure. Our study, a large pooled analysis of eight birth cohorts with data on more than 21,000 children, included 735 children who were exposed to maternal smoking only during pregnancy.

These children were at increased risk for wheeze and asthma at preschool age. Furthermore, the likelihood of developing wheeze and asthma increased in a significant dose-response pattern in relation to maternal cigarette consumption during the first trimester.”

The results, published in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine, came from an analysis of eight European birth cohorts, including a total of 21,600 kids. Parents were given questionnaires which authors used for exposure information and information on symptoms of wheeze and asthma.

The analysis showed that maternal smoking during pregnancy only 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 ages 4 through 6, after adjusting for factors such as parental education, siblings, sex, and birth weight.

Moreover, maternal smoking during the first trimester of pregnancy showed to have an effect on children’s development of wheeze and asthma; however, smoking during the third trimester or the first year of birth showed no increased risks.

Maternal smoking can begin to cause harm on the fetal respiratory system early in pregnancy, possibly before the mother even knows that she is pregnant, Dr. Neuman pointed out.

The research has a few limitations, such as the parents answering the questionnaires to obtain exposure and outcome information.

The author concluded:

“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.”

Although this study focused on the increased risks of developing wheeze and asthma, there are many other harmful risks for children whose mothers smoke. A few examples include:

  • stillbirth
  • low birth weight
  • prematurity
  • sudden infant death syndrome (SIDS)
  • high blood pressure
  • obesity in childhood and into adolescence

The expert warns, “Teens and young women should be encouraged to quit smoking before getting pregnant.”

Written by Sarah Glynn