Childhood asthma link shows it is never too soon for mums to quit smoking

Smoking during pregnancy increases the risk for asthma and wheezing in early childhood, even if children are not exposed to smoke after birth, a European study shows.

Researchers found that the risk for asthma was increased even in children of mothers who only smoked during the first trimester.

"This indicates that the hazardous effects of maternal smoking on the fetal respiratory system might present before the woman knows that she is pregnant," say Anna Bergstrom (Karolinska Institutet, Stockholm, Sweden) and colleagues.

They add that their findings should encourage public health efforts to get mothers to quit smoking before they fall pregnant.

The study included 21,600 children from eight European birth cohorts. An average of 23.5% of the children were exposed to maternal smoking during pregnancy or the first year of life, and 3.4% children were exposed during pregnancy but not after birth. The children were assessed by questionnaire at 4-6 years of age, at which time 10.4% experienced wheeze and 6.6% had asthma.

Compared with children who were never exposed to smoke, those exposed to maternal smoking only had a 39% increased risk for wheeze and a 65% increased risk for asthma.

Furthermore, in children who were only exposed during the first trimester, the risk rose by 45% for wheeze and 110% for asthma.

The authors also found a dose-response relationship for smoking consumption during pregnancy such that for every five additional cigarettes smoked per day, the risk for wheeze rose by 18% and the risk for asthma rose by 23%.

The authors believe theirs is the largest dataset regarding mothers' smoking and childhood respiratory disease to date.

"Our results… are in line with earlier findings. However, in none of the previous studies has the effect of pre- versus postnatal smoking been possible to disentangle from each other, mainly due to small sample size," they write in the American Journal of Respiratory and Critical Care Medicine.

They conclude that their findings have important consequences for public health: "Policy makers should be aware of the important role of motivating tobacco smoking teenage girls and young women to stop before getting pregnant to prevent asthma in their children."

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