To achieve a pregnancy many things are required. To begin with, a woman must produce an egg from her ovary. For this to occur a hormone called GnRH must be released from an area of the brain called the hypothalamus. This part of the brain is affected by outside influences and is why women with other illnesses or psychological problems may have difficulty conceiving.

The hormone GnRH acts on a gland at the base of the brain called the pituitary gland. This produces two hormones called FSH and LH. Disorders of the pituitary gland can affect this. For example, a condition called a prolactinoma which is a small tumor can interfere with FSH and LF production. Furthermore, abnormalities of the thyroid can result in an altered production of a hormone called TSH which is very similar to FSH and can distrupt the hormone balance.

The ovary releases an egg as a result of LH and FSH production. Other hormones produced by the ovary include, oestrogen, progesterone and testosterone. Abnormalities at the ovarian level just as the PolyCystic Ovarian syndrome (PCOS) can result in infertility.

Once an egg is produced it travels down the Fallopian tube where it is fertilised. A blocked tube can result in infertility and the most common causes of this are pelvic infections (such as chlamydia or gonorrhoea) and endometriosis.

For an egg to be fertilised a sperm must reach it. Abnormalities in sperm account for about a third of infertility problems.