Women

In women, infertility is most commonly linked to problems with ovulation. 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 years of age
• 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 (STIs) such as chlamydia can also affect the fallopian tubes. There may also be physical problems with the uterus, the presence of fibroids – non-cancerous clumps of tissue on the walls of the uterus – or endometriosis where tissue similar to the lining of the womb grows in other places such as the ovaries or fallopian tubes. 

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 or STIs such as gonorrhoea, can also cause problems, as can abnormally low levels of the male sex hormone testosterone.