This association was more pronounced in patients with moderate to severe disease, older patients, and patients who were not taking any therapy. The theory for this association involves system-wide inflammation, which is present in asthma. Inflammation of the fallopian tubes might be a factor in the delayed pregnancies seen in
asthmatic women. Supporting this theory is the fact that receiving asthma treatment designed to reduce inflammation reduces the time to achieve pregnancy.

Men with cystic fibrosis often have fertility problems. Less than 2% of men with cystic fibrosis can be fertile. In the vast majority of these men the conducting system for sperm (the so-called vas deferens) does not develop and is absent. There are ways around this problem but it underscores one of the many difficulties cystic fibrosis patients face.

In the case of asthmatic women of childbearing age, treatment should not be delayed not only due to concerns about pregnancy, but to prevent permanent lung damage.