Researchers found that pregnant women who experienced an asthma attack during the first trimester of pregnancy were 48% more likely to have a baby with at least one birth defect than pregnant women whose asthma was controlled.

Children of mothers who experienced an asthma flare up had a 12.8% rate of birth defects, while children of mothers with well controlled asthma had a rate of 8.9%.

During pregnancy a fetus needs a consistent supply of blood for normal growth and survival, particularly during the first trimester, a crucial period for fetal development. An asthma attack can create a drop in the level of oxygen in the blood for both mother and baby.

This analysis of over 4,300 pregnancies emphasizes the need to keep asthma well managed throughout pregnancy, and especially in the first trimester.

The research will be published in the June issue of the Journal of Allergy and Clinical Immunology.