Missed periods: common causes, when to see a GP and what tests involve

The NHS explains that for most women a period happens around every 28 days, but it is common for periods to be more or less frequent than this, from every 21 days to every 35 days. A period can last between 2 and 7 days and usually lasts about 5. Because cycles vary, a period that arrives a few days late is not necessarily a missed period.

The NHS also notes that sometimes the gap between periods just varies each time, so periods come early or late. This is known as having irregular periods. A period that does not come at all for a month or more is generally called a missed period, and if periods stop for several months the term used is absent periods or amenorrhoea.

The NHS lists a range of common causes. Many of them are not illnesses at all, but changes in the body or in life circumstances that affect the hormones controlling the cycle.

• Being pregnant.

• Stress.

• The start of the menopause (perimenopause), usually between the ages of 45 and 55.

• Polyendocrine metabolic ovarian syndrome (PMOS), which used to be called polycystic ovary syndrome (PCOS).

• Sudden weight loss, or being overweight.

• Doing too much exercise.

• Certain hormonal methods of contraception, such as the contraceptive pill, injection or intrauterine system (IUS).

• Breastfeeding.

The NHS says periods can also sometimes stop as a result of a medical condition such as heart disease, diabetes, or an overactive or underactive thyroid. These are usually accompanied by other symptoms, which is why a GP will ask about your general health rather than focusing only on the periods.

The NHS lists other symptoms that, together with a missed period, are a reason to see a GP: weight gain or weight loss, tiredness, hair growth on the face, and dry or oily skin.

The NHS says you could be pregnant if you miss a period and have had sex. A home pregnancy test is the quickest way to find out. If the test is negative and your period still does not arrive, the NHS advises seeing a GP if you have missed 3 consecutive periods, and they will investigate the cause and recommend any necessary treatment.

Hormonal contraception can also make periods lighter or stop. This is not a problem in itself, but if you are not sure whether your contraception is the explanation, a GP, nurse or pharmacist can help you work it out.

The NHS says to see a GP if you have missed your period 3 times in a row, if your periods have not started by the time you are 15, if you have missed a period and have other symptoms such as weight gain or loss, tiredness, hair growth on your face and dry or oily skin, or if your periods have become irregular.

The NHS also says that bleeding between periods, bleeding after sex or bleeding after the menopause needs to be checked by a doctor. Changes in your periods, such as lasting longer or getting lighter, do not necessarily mean there is a problem but do need to be investigated.

The NHS says a GP will ask about your health and may do some blood tests to find the cause. They may refer you to a specialist (a gynaecologist or endocrinologist) if you need more tests or scans. Some people keep a simple diary of period dates, weight changes and symptoms for a few months before the appointment, which can make the history clearer.

The assessment aims to find out whether the missed periods have an ordinary explanation, such as stress or weight change, or whether a condition such as PMOS or a thyroid problem needs treating.

Treatment depends on the cause. The NHS gives examples: the combined contraceptive pill to help make periods more regular if you have a condition like PMOS, and hormone replacement therapy (HRT) if you are starting the menopause. A GP can also give advice or therapy to help reduce stress and to maintain a healthy weight.

Where the cause is lifestyle-related, periods often return once the underlying factor is addressed. Where it is a condition such as PMOS or thyroid disease, treating that condition is the main approach.