Asthma during pregnancy: mechanisms and treatment implications.

Asthma is becoming increasingly prevalent worldwide. Numerous historical and prospective cohort studies have investigated the effects of maternal asthma on pregnancy outcome; however, the data has been conflicting and many studies have not used standard classifications for asthma severity. Overall, the literature suggests that asthmatic females are more at risk of low birth weight neonates, pre-term delivery and complications such as pre-eclampsia, especially in the absence of actively managed asthma treated with inhaled corticosteroids. Pregnancy with a female foetus may particularly increase the risk of these outcomes. In addition, pregnancy has an effect on the course of asthma. The risk of an exacerbation requiring medical intervention may be as high as 50% in females with severe asthma and this may further increase the risk of poor outcomes, particularly low birth weight and pre-term delivery. The mechanisms responsible for changes in asthma with pregnancy, or alterations in pregnancy outcomes due to asthma have not been thoroughly explored. Maternal inflammatory pathways may contribute to reduced foetal growth through alterations in placental function. Asthma treatment, by reducing maternal inflammation and preventing exacerbations, is safe for use in pregnant females and contributes to improved outcomes for both mother and foetus.