Women with asthma should not leave it too late to have a baby, experts have warned, after research suggested they may need extra help conceiving.

A study of almost 3,000 women found that 12 per cent of those with asthma needed fertility treatment compared to seven per cent of those without.

Experts said the study does not prove that asthma reduces fertility in women, but may suggest that better control of their symptoms could help them conceive more easily.

The research was presented at the European Respiratory Society International Congress in Milan.

Experts from Hvidovre Hospital in Denmark examined data for 744 pregnant women with asthma who gave birth between 2007 and 2013, and compared it with data from women without asthma over the same period, who acted as a control group.

Charlotte Suppli Ulrik, from the hospital’s department of respiratory medicine, said: “We don’t have the hard-core evidence, but based on what we know, it seems very likely that good asthma control will improve fertility in women with asthma by reducing the time it takes to become pregnant and, therefore, the need for fertility treatment.

“However, age is a crucial factor so the message, particularly for women with asthma, is don’t wait too long, as it might reduce your chances of having children.”