Since sperm and eggs need to come together in the tube for pregnancy to occur, infertility can be caused by any factor that affects egg release, sperm quality or tubal health.
Anovulation refers to the failure to release an egg. Over 80% of cases are due to polycystic ovarian syndrome (PCOS). For more information see my sections on Anovulation and Ovulation Induction and PCOS.
Poor quality sperm contribute to 20-40% of cases of infertility. Sperm defects vary in severity from relatively mild to the most severe form in which, sperm production is completely absent. In the latter case, there will be no sperm in the ejaculate (known as azoospermia). For more information on sperm and the conditions that can affect sperm quality, see my Section on Male Infertility and Sperm.
The main causes of tubal damage are infection, previous pelvic surgery and endometriosis.
Pelvic inflammatory disease (PID) caused by “bugs” such as chlamydia and gonorrhoea lead to scarring and blockage of the Fallopian tubes. Even if the tubes remain open, their function could be severely compromised by infection. Some of the tell-tale signs of PID include pelvic pain, fever and an abnormal vaginal discharge. In some cases, infection may remain silent and only become discovered during a workup for infertility.
Surgery in the vicinity of the Fallopian tubes can also result in tubal scarring. The appendix often sits very close to the right Fallopian tube. Consequently, surgery for removing the appendix (appendicectomy) can result in tubal damage, especially if appendicitis led to a ruptured appendix. Another form of surgery that can affect the tubes is surgery for ovarian cysts.
Deposits of endometriosis in the vicinity of the Fallopian tubes may cause inflammation and scarring that envelops the tube. For more information see my section on Endometriosis.
In around 20-30% of couples, no abnormality is identified with ovulation, sperm or tubes. This is referred to as unexplained infertility. It is not a very accurate term and only means that standard tests for infertility (see below) have not identified any major abnormality. However, a cause for the couple’s infertility often emerges after the couple have embarked on fertility treatment. For instance, if IVF is undertaken, it may become apparent that there is a problem with the ability of the sperm to fertilise the egg. For more information, see my section on IVF/ICSI Treatment.