Sydney : Many pregnant asthmatic women, who may be remiss in using the right medication, may end up risking the health of their unborn child, a study reveals.

If asthma is not correctly managed during pregnancy it can result in premature births, low birth weights and even stillbirths, said postdoctoral researcher Annette Osei-Kumah from University of Adelaide.

Asthma is often worse during pregnancy due to different factors released from the placenta which cause inflammation in the mother's lung, said Osei-Kumah.

Previous studies reveal that during pregnancy, one-third of women report their asthma is worse, one-third maintain their asthma remains the same and another third report an improvement, said a university statement.

However, most women underestimate the effect of asthma during their pregnancy, said Osei-Kumah.

"Most women who said their asthma didn't change actually recorded poorer lung function when tested, and 55 percent experienced at least one asthma attack during pregnancy," she said.

There are sex-specific effects as well. Uncontrolled asthma invariably leads to low birth weights in female babies. Male babies, on the other hand, continue to grow normally but if a mother has an asthma attack during pregnancy they are less likely to survive.

Most women who are asthmatic stop using their medications during pregnancy due to fear of side-effects, but their concerns are unfounded, added Osei-Kumah.