A study of 5,000 women in Australia, New Zealand, the UK and Ireland found those who only used their inhaler in an emergency rather than taking it to prevent an attack took longer to get pregnant.
Researchers at the University of Adelaide in Australia found that women only using short-term medication – or short-acting beta-agonists – took 20 per cent longer to conceive on average.
They were also 40per cent more likely to take more than a year to conceive – which the researchers defined as the threshold for suffering infertility.
The difference remained even when other factors such as age and weight were taken into account. But the same study found that women who took long-acting acting asthma preventers on a regular basis even when they were not experiencing symptoms were as likely to conceive as other women.
All of the participants were expecting their first babies and were in the early stages of pregnancy. They were asked if they were suffering from asthma, and which medicines they used.
Ten per cent of the participants had asthma, and on average they were found to take longer to get pregnant. But the researchers said there was no difference between women using long-acting treatments and women without asthma.
At this stage it is not yet known why asthma-relievers could have an impact on fertility while long-term asthma treatment medications do not, but it could be due to inflammation in the reproductive organs caused by asthma.
Lead researcher Dr Luke Grzeskowiak said: “There is plenty of evidence that maternal asthma has a negative impact on the health of pregnant mothers and their babies, and so our general advice is that women should take steps to get their asthma under control before trying to conceive.”
He added: “What we don’t yet know is exactly how asthma or asthma treatments lead to fertility problems.
“As well as affecting the lungs, asthma could cause inflammation elsewhere is the body, including the uterus. It could also affect the health of eggs in the ovaries.
“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.”
The researchers said the results did not include women from the time they were trying to conceive, so it excluded women who were unable to conceive naturally.
The research team are now planning further studies involving women with asthma who are undergoing fertility treatments, to see whether improving asthma control could also improve fertility.