Causes of infertility

Human reproduction depends on fertility (the ability to conceive) and the capacity to maintain a fetus in utero. It requires:

• production of gametes (sperm and oocytes) capable of fertilisation
• release of the oocyte into a patent fallopian tube after ovulation
• timely deposition and migration of sufficient fertile sperm in the female reproductive tract to enable fertilisation
• implantation and development of the embryo in the hormonally primed uterine mucosa
• maintenance of the growing fetus in the uterus until it is fully viable.

Infertility may be due to factors in the female partner (in about 40% of couples), the male partner (in about 40% of couples), both partners or unexplained factors.

In females, causes of impaired fertility include:

• anovulation from a range of causes, most commonly polycystic ovarian syndrome
• endometriosis causing tubal obstruction, changes to endometrial function and reduced sexual activity due to pain
• tubal obstruction and uterine anomalies.

In males, causes of impaired fertility include:

• failed spermatogenesis (which may be primary [testicular] or central [pituitary or hypothalamic])
• reduced numbers or motility, or changed morphology of the sperm
• failed delivery of sperm, due to obstruction of the vas deferens (as occurs in congenital bilateral absence of the vas deferens in cystic fibrosis), or a testicular tumour, or erectile or ejaculatory failure).