Anovulation: when ovulation does not happen, and what it means for periods and fertility

Ovulation is the monthly release of an egg from an ovary. Anovulation is when that does not happen in a cycle. Some people ovulate only occasionally, which doctors may call oligo-ovulation, while others do not ovulate at all. The NHS lists lack of regular ovulation among the common causes of infertility, alongside poor quality semen, blocked or damaged fallopian tubes and endometriosis.

Because ovulation drives the hormonal rhythm of the menstrual cycle, anovulation often shows up as periods that are irregular, infrequent or absent, although bleeding can sometimes occur without ovulation. A blood test, rather than just a calendar, is therefore used to check.

The NHS describes irregular periods as a gap between periods of less than 21 days or more than 35 days, and says the average gap is around 28 days. Irregular periods are more likely when periods first start at puberty and when nearing menopause. It suggests keeping a diary or app to track your periods.

You may notice any of the following, though none proves that you are not ovulating:

• periods that are irregular, far apart or missing

• difficulty getting pregnant after a year of regular unprotected sex

• extra hair growth on the face or body, oily skin or acne, which can come with polyendocrine metabolic ovarian syndrome (PMOS)

• weight gain, tiredness or other symptoms of a thyroid or hormone problem

The NHS lists common causes of irregular periods that are also relevant to ovulation: puberty, the start of menopause (usually between the ages of 45 and 55), pregnancy, hormonal contraception such as the progestogen-only pill, injection and intrauterine system, losing or gaining a lot of weight, stress and anxiety, and exercising too much.

Conditions can also be responsible. The NHS names polyendocrine metabolic ovarian syndrome (PMOS), which used to be called polycystic ovary syndrome (PCOS), and thyroid problems. It describes PMOS as a hormone condition that can affect hair growth, periods, fertility and mood, and says problems getting pregnant are usually because the ovaries do not release an egg each month. The cause of PMOS is unknown, but it may be to do with hormones such as insulin and testosterone not working properly.

Other NHS-listed risk factors for fertility problems that can interfere with ovulation include being overweight or severely underweight, smoking, drinking too much alcohol, stress in severe cases and age.

The NHS advises seeing a GP if you have not conceived after a year of trying, or sooner if you are 36 or over or have other concerns such as previous cancer treatment. The GP asks about your periods, previous pregnancies, contraception, medicines, weight and lifestyle, and may examine you or refer you for tests.

To check whether you are ovulating, the NHS says a blood sample can be tested for progesterone, with the timing based on how regular your periods are. If your periods are irregular you will be offered a test to measure gonadotrophins, the hormones that stimulate the ovaries to produce eggs. Other tests include a chlamydia test and an ultrasound scan to check the ovaries, womb and fallopian tubes.

For suspected PMOS, the NHS says tests include blood tests to check hormone levels and insulin resistance and an ultrasound scan of the ovaries, which is only done if you are over 18.

Treatment depends on the cause and on what is funded locally. The NHS lists three main types of fertility treatment: medicines, surgical procedures and assisted conception such as intrauterine insemination (IUI) and IVF. For lack of regular ovulation the first step is usually medicine.

According to the NHS, clomifene encourages the monthly release of an egg in women who do not ovulate regularly or cannot ovulate at all. Tamoxifen is an alternative if you have ovulation problems, metformin is particularly beneficial for women who have PMOS, and gonadotrophins and other hormone-acting medicines can help stimulate ovulation. Side effects can include nausea, vomiting, headaches and hot flushes.

If ovulation medicine has not worked in PMOS, the NHS says a minor surgical procedure called laparoscopic ovarian drilling, which uses heat or a laser to destroy part of the ovary, may be used. It also notes that medicine that stimulates the ovaries is not recommended for women with unexplained infertility because it has not been found to increase their chances of getting pregnant.

If the cause is a lifestyle factor such as weight change, excessive exercise or stress, addressing it may help restore ovulation. For PMOS, the NHS suggests a healthy balanced diet, regular exercise, losing weight if overweight and talking therapy where mood is affected.

Not ovulating can still matter if you are not planning a pregnancy. The NHS advises seeing a GP if your periods are irregular, last longer than 7 days, come with other symptoms such as weight gain, tiredness, facial hair growth or dry or oily skin, or you have bleeding between periods. Treatment is not always needed, and if it is, it depends on the cause. For example, if PMOS is causing irregular periods the combined pill may help to make periods more regular.

The NHS notes that PMOS can raise the risk of conditions including type 2 diabetes, high blood pressure, cardiovascular disease, non-alcoholic fatty liver disease and womb cancer, and that regular check-ups can reduce the risk.

The NHS says the treatment offered depends on the cause and on what is available from your local integrated care board, and that if a GP refers you to a specialist for tests the NHS will pay for this. Funding for assisted conception varies across the UK and waiting lists can be long in some areas.

Private treatment is available but, as the NHS warns, it can be expensive and there is no guarantee that it will be successful. It advises choosing a clinic carefully and making sure it is licensed by the Human Fertilisation and Embryology Authority, asking about success rates, waiting times and a fully costed plan.