Irregular periods: causes, symptoms, treatment and when to see a GP

The NHS lists these common causes of irregular periods:

• puberty, when you start your periods

• the start of menopause, usually between the ages of 45 and 55

• pregnancy, because a missed period is often an early sign

• hormonal contraception such as the progestogen-only pill, contraceptive injection and intrauterine system (IUS)

• losing or gaining a lot of weight

• stress and anxiety

• exercising too much

The NHS says that conditions such as polyendocrine metabolic ovarian syndrome (PMOS), which used to be called polycystic ovary syndrome (PCOS), or thyroid problems can sometimes cause irregular periods.

The NHS PMOS page describes irregular periods or long gaps between periods as one of the main symptoms, alongside excessive hair growth or hair loss, weight gain or difficulty losing weight, difficulty getting pregnant, mental health problems such as depression or anxiety, oily skin and acne, feeling very tired, and thick dark patches of skin on the neck or armpits. It says the cause is unknown but may involve hormones such as insulin and testosterone not working properly.

The NHS missed or late periods page adds that periods can also stop as a result of a medical condition such as heart disease, diabetes, or an overactive or underactive thyroid.

Irregular periods themselves are the symptom: the gap between periods varies, or they come earlier or later than expected. The NHS suggests using an app or a diary to track periods. Day 1 of your cycle is the first day of your period, and the last day is the day before your next period begins.

Other symptoms matter because they may point to a cause. The NHS says to see a GP if you have irregular periods with weight gain, tiredness, hair growth on your face, or dry or oily skin, or if you have bleeding between periods.

The NHS says treatment is not always needed for irregular periods. A GP may refer you to a specialist if you need tests to find out what is causing them. If treatment is needed, it depends on the cause.

For example, if PMOS is causing irregular periods the combined pill may help make your periods more regular, and if other hormone problems such as thyroid problems are the cause, medicines can help treat it. For perimenopause, the NHS missed periods page mentions hormone replacement therapy (HRT), and a GP can also give advice or therapy to help you reduce stress and maintain a healthy weight.

The NHS PMOS page also lists the progestogen-only pill or an IUS to help with irregular periods, clomifene to improve fertility, and lifestyle measures including a healthy balanced diet, regular exercise and weight loss if you are overweight.

The NHS says the average gap between periods starting is around 28 days, and it can sometimes be a bit shorter or longer. A woman's periods are irregular if the gap between them is less than 21 days or more than 35 days.

The NHS periods page says it is common for periods to be more or less frequent than every 28 days, ranging from every 21 days to every 35 days, and that a period usually lasts about 5 days and can last between 2 and 7 days. It also says irregular periods can affect anyone who has periods.

The NHS says it is more likely for periods to be irregular when they first start during puberty and when you are nearing menopause. It says most girls will have regular periods by age 16 to 18, and that a delay in starting periods is not usually a cause for concern.

If irregular periods continue for several cycles outside puberty and menopause, or a new pattern develops, speak to a GP. The NHS says a change in your periods, such as lasting longer or getting lighter, does not necessarily mean there is a problem but does need to be investigated.

The NHS says you could be pregnant if you miss a period and you have had sex, and that a missed period is often an early sign of pregnancy. See a GP if you have taken a pregnancy test and the result is negative and you have missed 3 periods in a row.

If you are trying for a baby, the NHS says getting pregnant can be more difficult with irregular periods because you might not release an egg (ovulate) regularly. It can help to have sex every 2 or 3 days throughout your cycle. If you are struggling to get pregnant you may be referred for further tests, and hormone medicine or fertility treatment may be recommended.

The NHS says to see a GP if:

• your periods are irregular

• your periods last longer than 7 days

• you have irregular periods and other symptoms such as weight gain, tiredness, hair growth on your face, and dry or oily skin

• you have bleeding between periods

• your periods are irregular and you are struggling to get pregnant

On the NHS, a GP can arrange blood tests and refer you to a gynaecologist or endocrinologist if more tests or scans are needed. You can also see a sexual health or contraceptive clinic. Some people choose a private gynaecology or hormone consultation for quicker scans and tests. The same causes and treatments apply, and results should be shared with your GP so your record is complete.