Smoking While Pregnant Linked to Asthma

Past research has already shown links between mothers who smoke and asthma in their children. But what if a mom only smokes while pregnant and quits before giving birth?

According to a recent study, her child is still at a higher risk for developing wheeze and asthma — especially if the mother smoked during her first trimester of pregnancy.

Don't smoke during pregnancy.

The study was led by Åsa Neuman, MD, of the Institute of Environmental Medicine at Karolinska Institutet and the Department of Women's and Children's Health at Uppsala University Hospital, both located in Sweden.

The researchers already knew that tobacco exposure during a child's early life or during pregnancy could increase the risk of asthma or wheeze, but they didn't know what differences in risk existed with prenatal-only exposure compared to being exposed after birth.

Therefore, Dr. Neuman and her colleagues tracked 21,600 children who were part of eight different European groups followed from birth.

A total of 735 children (3.4 percent of the total group) had been exposed to their mothers' smoking while they were in the womb but not after they were born.

The researchers gathered information on the children's symptoms of wheezing and asthma from parent questionnaires.

They also took into account the children's gender, their birth weight, their number of siblings and their parents' education levels as well as whether their parents had asthma.

The researchers found that children of women who smoked only during pregnancy — but not afterward — were at a higher risk for wheezing and for asthma when they were 4 to 6 years old. The children were 1.4 times more likely to have wheeze and 1.65 times more likely to have asthma.

Further, women who smoked during their first trimester, but who did not smoke in their third trimester or in their child's first year of life, also had children with a higher risk for wheeze and asthma.

In fact, the more a woman smoked during her first trimester of pregnancy, the more likely it was that her child would have wheeze or asthma.

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

"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. Teens and young women should be encouraged to quit smoking before getting pregnant," she said.

The study was published August 17 in the American Journal of Respiratory and Critical Care Medicine. The research was funded by a grant from the European Community’s Seventh Framework Program. The authors did not note any conflicts of interest.