Infertility can be caused by many different factors. In general, about a third of infertility cases can be linked to a problem with the woman and another third to problems with her male partner. In some, multiple factors may be to blame or an exact cause may never be identified.

Infertility in women

In women, infertility is most commonly linked to problems with ovulation €“ the release of the egg from the ovary. Polycystic ovary syndrome (PCOS) is a common cause, where hormonal imbalances interfere with normal ovulation. Another possible cause is primary ovarian insufficiency (POI), when a woman's ovaries stop working normally before she is 40. Thyroid problems can also prevent ovulation. Some women suffer from blocked oviducts as a result of pelvic inflammatory disease or a previous ectopic pregnancy. There may also be physical problems with the uterus or the presence of fibroids €“ non-cancerous clumps of tissue on the walls of the uterus. Women with any of the following should talk to a GP:

• Irregular or missed periods
• Very heavy or painful periods
• Endometriosis
• Pelvic inflammatory disease
• Previous ectopic pregnancy
• More than one miscarriage.

Infertility in men

Male infertility is usually linked to the number or quality of the sperm produced, or to physical issues that may reduce sperm mobility. A low sperm count, reduced sperm mobility or a high percentage of abnormal sperm are all possible factors. Any condition that affects or damages the testicles can also cause problems, as can abnormally low levels of the male sex hormone testosterone. Men who know they have a history of any of the following should seek medical advice before starting a family:

• Testicular cancer
• An infection of the testicles
• Surgery or injury involving the testicles
• A congenital defect affecting the testicles or when the testicles have not descended into the scrotum.