Published: 20-08-2012 00:00 | Updated: 09-06-2015 10:45

Smoking during pregnancy increases risk of asthma in 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 where scientists at the Institute of Environmental Medicine at Karolinska Institutet have participated.

The eight European birth cohorts that were included in the study involved more than 21,000 children. In total, over 20 percent of the children were exposed to maternal smoking in fetal life and during the first year after birth, of which 735 (3 percent of the children) only during pregnancy. Exposure information and information on symptoms of wheeze and asthma were derived from parental questionnaires.

"Earlier epidemiological studies suggest that exposure to maternal smoking during fetal and early life increases the risk of childhood wheezing and asthma, but our study is the first one that differentiate the effects of prenatal and postnatal exposure", says Dr Anna Bergström of the Institute of Environmental Medicine.

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 and asthma at age four to six years. Further, 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 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", says Dr Bergström. "Therefore teens and young women should be encouraged to quit smoking before getting pregnant."

The study was conducted within the ENRIECO consortium (Environmental Health Risks in European Birth Cohorts), funded by the EU's Seventh Framework Programme. In addition to the scientists from Sweden, research groups from Denmark, the Netherlands, Spain, the UK, and Germany took part in the study.


Maternal smoking in pregnancy and asthma in preschool children: a pooled analysis of eight birth cohorts.
Neuman �, Hohmann C, Orsini N, Pershagen G, Eller E, Kjaer H, et al
Am. J. Respir. Crit. Care Med. 2012 Nov;186(10):1037-43