Pregnant women who fail to manage their asthma with the right medication are risking the health of their unborn children.
If mismanaged, aggravated asthma could affect the foetus, with side effects ranging from premature births to stillborns.
The gender of the unborn child also has an impact. Females are more likely to be affected by mismanaged asthma, while males appear to be unaffected.
The study shows that pregnancy can aggravate pre-existing asthma, due to the placenta releasing factors which irritate and inflame the lungs.
The researchers argue that asthmatic mothers-to-be should maintain their medication, as their fears of medical side-effects are unfounded.