Adelaide, Australia—Women with asthma who seek to become pregnant might do better using long-acting asthma preventers instead of short-acting asthma relievers.

That’s according to a new study in the European Respiratory Journal, which finds that patients using only beta-agonists took 20% longer to become pregnant than other women.

On the other hand, University of Adelaide–led research noted that data from more than 5,600 women in Australia, New Zealand, the United Kingdom, and Ireland also indicate that women with asthma conceive as quickly as other women when they use inhaled corticosteroids to prevent symptoms. 

“Five to ten per cent of all women around the world have asthma and it is one of the most common chronic medical conditions in women of reproductive age,” explained Luke Grzeskowiak, PhD, BPharm. “Several studies have identified a link between asthma and female infertility, but the impact of asthma treatments on fertility has been unclear.”

For the study, researchers examined data from the international Screening for Pregnancy Endpoints (SCOPE) study, which included participants in the early stages of pregnancy who were expecting their first babies. One out of 10 women in the study said she had asthma and, overall, took longer to get pregnant.

When the type of asthma treatments being used was analyzed, no difference in fertility was documented between women using long-acting asthma treatments and women without asthma.

Yet, women using short-acting asthma-relief medication were 30% more likely to have taken more than a year to conceive, which the researchers defined as the threshold for infertility. That difference persisted even when other factors—such as age and weight—were taken into consideration.

“What we don’t yet know is exactly how asthma or asthma treatments lead to fertility problems,” Grzeskowiak notes. “As well as affecting the lungs, asthma could cause inflammation elsewhere in the body, including the uterus. It could also affect the health of eggs in the ovaries.”

He suggested a possible explanation, explaining, “Inhaled corticosteroids suppress the immune system, whereas short-acting asthma treatments do not alter immune function. In women who are only using relievers it’s possible that, while their asthma symptoms may improve, inflammation may still be present in the lungs and other organs in the body.”