Smoking while pregnant has been found to dramatically increase the asthma risk in newborns.
Researchers in Sweden said that the risk of developing asthma is 65 percent higher in kids whose mothers smoked while pregnant.
The study of over 20,000 children said that the risk is increased even if the child is no longer exposed to smoke, said Health Day.
"These children were at increased risk for wheeze and asthma at preschool age," said Asa Neuman, of the Karolinska Institute in Stockholm, Sweden, reported Medical News Today.
"Furthermore, the likelihood of developing wheeze and asthma increased in a significant dose-response pattern in relation to maternal cigarette consumption during the first three months of pregnancy."
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The risks stood even as other factors such as weight, gender and education level of the parents was controlled for, reported the Daily Mail.
The authors said that the mother may not even know she is pregnant while she's smoking.
"These results indicate that the harmful effects of maternal smoking on the fetal respiratory system begin early in pregnancy, perhaps before the women is even aware that she is pregnant," Neuman said, according to Health Day.
The study was published in the American Journal of Respiratory and Critical Care Medicine.