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. Common hormonal causes preventing ovulation include polycystic ovary syndrome, where hormonal imbalances interfere with normal ovulation; primary ovarian insufficiency (early menopause), when a woman’s ovaries stop working, normally before she is 40; or thyroid problems. Some women suffer from blocked fallopian tubes as a result of pelvic inflammatory disease or a previous ectopic pregnancy, and some sexually transmitted infections such as chlamydia can also affect the fallopian tubes. 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 who want to conceive but have 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 a low sperm count, reduced sperm mobility and/or a high percentage of abnormal sperm. Any condition that affects or damages the testicles, such as mumps, can also cause problems, as can abnormally low levels of the male sex hormone testosterone.
 
Men with a history of any of the following should talk to a GP 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 they have not descended into the scrotum.