Cystic Fibrosis is a genetic condition caused by inheriting two pathologic genes from both parents. In males, CF may cause structural and anatomical abnormalities in the reproductive tract, like vas deferens agenesis (absence of sperm duct). This, clinically, translates to undisturbed sperm production in the testes, which, however, is not ejaculated.

CF testing may also be performed in the context of genetic counseling, since if both partners are CF carriers (they each have one abnormal gene and are healthy), there is a 25% chance that the offspring will have the condition (will have inherited both abnormal genes). In such cases, pre-implantation genetic testing is advised. There are many mutations that may cause CF, but the most commonly recommended test assesses only one, delta F508, which accounts for 60-70% of all cases. However, in cases of elevated clinical suspicion, or when one partner has already been diagnosed as a CF carrier, a more thorough assessment with multiple mutation testing may be recommended, in order to exclude the possibility of CF with 99% certainty.