One cause of infertility is infrequent ovulation or ovulation not happening.

This is most commonly due to Polyendocrine Metabolic Ovarian Syndrome (PMOS), and 9% of women have PMOS. Women who have PMOS often have increased facial or body hair, acne, infrequent or absent periods. They may be lean or obese but PMOS is always worsened by weight gain or obesity.

Another cause of absent or infrequent ovulation is elevation of the hormone prolactin. Prolactin is produced by the pituitary gland (a pea sized gland located at the base of the brain) when breast-feeding. Prolactin can be increased by certain drugs and by treatable tumours of the pituitary gland which are usually benign. High levels of prolactin can be treated generally with medication.

Sometimes a woman may not be ovulating because she has very greatly reduced numbers of eggs in the ovary. This is sometimes called reduced ovarian reserve or, when the eggs are almost absent, premature ovarian failure or premature menopause. The most common way women with very low or absent eggs achieve a pregnancy is through the use of eggs donated by another woman.

The fallopian tubes can sometimes be blocked or injured. The fallopian tubes transport the egg to the uterus and it's in the fallopian tube that fertilisation of the egg by the sperm usually occurs.

The tube is responsible for the nutrition and transport of the fertilised egg to the uterus where it implants.

Fallopian tubes get blocked or injured in a number of ways such as:

• Sexually transmitted infection - repeated infections of gonorrhea or chlamydia damage the tubes
• Endometriosis
• Appendicitis - if the appendix perforates or bursts, it can impact the fallopian tubes
• Surgery

It’s possible for the fallopian tubes to be open but scarred and therefore don’t allow the transfer of the fertilised egg to the uterus at the correct time. This can lead to an ectopic or tubal pregnancy or hydrosalpinx.

Endometriosis is a complex disorder, which can occur without pain or can cause pelvic pain which can be worse during menstruation or sometimes painful intercourse.

The association with endometriosis and infertility is complex and treatment needs to be carefully considered.

Endometriosis is the tissue which normally lines the uterus (called the endometrium) is in parts of the body other than the uterus. Endometriosis commonly occurs in the membrane, which lines the abdomen and pelvis, which is called the peritoneum. These often respond to the hormonal changes of each menstrual cycle and cause scarring. It is uncertain how common endometriosis is but it may occur in minor or mild forms in up to 25% of women. Severe endometriosis is much less common. Endometriosis is often associated with adenomyosis and this is now a recognised contributor to the infertility seen with endometriosis.

Abnormalities of the uterus can contribute to delay in conceiving.

Some abnormalities include:

• Fibroids - which begin as tumours of the muscle of the uterus. They occur in one in three women and don’t always contribute to infertility. It's important that the fibroids are carefully evaluated and the treatment of the fibroids is carefully discussed with the woman and her partner.
• Scarring of the uterus lining - sometimes can occur after a miscarriage requiring curettage or a termination of pregnancy. This is rare and needs to be carefully evaluated as treatment is often difficult.
• Septum or shelf of extra tissue in the uterus - is uncommon, but contributes to early pregnancy loss and miscarriage.
• Previous surgery to the cervix for treatment of papilloma or wart virus infection - the loss of mucous glands of the cervix following this surgery may reduce natural fertility.
• Adenomyosis - where the lining of the uterus grows into the muscle and causes heavy periods. Adenomyosis is associated with infertility, reduced success in IVF and miscarriage.
• Polyps within the lining of the uterus - can cause bleeding between periods. The way in which polyps contribute to infertility is uncertain but removal has been shown to be beneficial for fertility and is recommended.

Sometimes a woman may have a low number of eggs in the ovary.

This is often detected by measurement of the anti-mullerian hormone (AMH). A low level of AMH means that fewer eggs will collected during an IVF cycle. Genetic tests should be performed if the AMH is reduced greatly for the age of the woman.

If a woman is young she may have good quality embryos despite a reduced number of eggs. Sometimes eggs do not form good quality embryos in the laboratory and it can be difficult to treat this problem. The reduction of the dose of FSH and/or a different preparation of FSH can help with this problem or there are extra medications which can help if the woman with reduced ovarian reserve is undertaking IVF.