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A couple is considered infertile when they have not conceived after a full year of regular sexual intercourse without contraception. About one-third of all cases of infertility are related to male factors, and an equal number are due to factors in women. The remaining cases are either related to problems in both partners or occur for unknown reasons.

Men are considered infertile if they produce no sperm cells, if they produce too few sperm cells, or if their sperm cells are abnormal or die before they can reach the egg. Chronic problems with ejaculation also contribute to male infertility. In rare cases, infertility in men is caused by an inherited condition, such as cystic fibrosis or chromosomal abnormalities.

Most infertility cases are treated with conventional medical therapies such as medication or surgery. Assisted reproductive technologies, for example, in vitro fertilization and similar treatments, account for less than 5% of infertility services. Infertility, which is often a reversible or treatable condition, should be distinguished from sterility, which implies an irreversible inability to conceive.