It also increases the risk of miscarriage. Sometimes endometriosis has no symptoms, but for many women it causes painful periods, pain during intercourse, and abnormal menstrual bleeding. Symptoms of ovulation disorders include infrequent or irregular periods and either extremely heavy or extremely light menstrual bleeding. For sperm to enter the cervix and survive long enough to fertilize an egg, the mucus at the entrance to the cervix needs to have a particular chemical composition and texture. Some women, often because of an infection or hormonal problems, don't produce the right amount or quality of cervical mucus for this process to successfully occur.
Some women produce immune proteins called antibodies that react with sperm.
And some men produce antibodies against their own sperm. Sperm allergies produce no symptoms. In nine out of 10 cases of male infertility, the problem stems from abnormal sperm production. A small number of men produce no sperm. Others have a low sperm count, although that doesn't necessarily make a man infertile.