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.
Previous studies have suggested that maternal smoking during foetal and early life increases the risk of childhood wheezing and asthma, but did not differentiate between the effects of prenatal and postnatal exposure.
Swedish researchers examined data on data on more than 21,000 children, included 735 children who were exposed to maternal smoking only during pregnancy. Exposure to smoke and information on symptoms of wheeze and asthma were derived from parental questionnaires.
The results published online ahead of print publication in the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine showed that maternal smoking only during pregnancy was associated with 39% increased risks for wheeze and 65% increased risk of asthma at age four to six years.
Furthermore, 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.
Commenting on the results for children exposed to smoke only prenatally, Lead author Dr Åsa Neuman, of the Institute of Environmental Medicine at the KarolinskaInstitutet in Stockholm, Sweden, said: "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.
"These results indicate that the harmful effects of maternal smoking on the foetal respiratory system begin early in pregnancy, perhaps before the woman is even aware that she is pregnant."