These Y-shaped molecules have an important task in the body. They mediate the defense from bacteria and viruses by recognizing and binding to very small structures on their surfaces. The antibodies are responsible for the inability to conceive if they can be found in the mucus that is typically formed in the uterine neck prior to the ovulation (the so called cervical mucus).  This mucus is viscous and, several days before ovulation, thready. Some women use these signs to identify their fertile days.

The presence of sperm-targeting antibodies in the cervical mucus can be a reason why some couples may be unable to become pregnancy.