Period flooding: what it means, causes and when to see a GP

People who search for period flooding are usually describing the same experience: blood that comes so quickly that a pad or tampon fills within an hour or two, that leaks onto clothes or bedding, or that arrives with large clots. It can happen without warning, in public, or overnight, and it is frightening and embarrassing for many people.

The NHS does not use the word flooding, but its description of heavy periods covers the same ground. It says you may have heavy periods if you need to change your pad or tampon every 1 to 2 hours, need to use two types of product together, have periods lasting more than 7 days, pass blood clots larger than about 2.5cm, or bleed through to your clothes or bedding. It also lists avoiding daily activities such as exercise, taking time off work, and feeling tired or short of breath a lot.

Importantly, the NHS adds that many women have heavy periods and that they may be normal for you. What matters clinically is the effect on your life and whether the pattern has changed.

Patient.info explains that it is often difficult to know whether periods are normal or heavy compared with other women. It gives a normal blood loss as between 30 and 40 ml per month, with bleeding lasting up to eight days and five days being average, and describes a heavy period as a loss of 80 ml or more, about half a teacupful. It also points out that some women who feel their periods are heavy actually have an average loss, and the reverse can also be true.

Because nobody measures their flow in millilitres, the practical signs matter more. Patient.info lists bleeding through to clothes or bedding, changing pads or tampons every hour, needing double protection, soaking bedclothes, passing large clots and restrictions on normal life. Most of the loss usually happens in the first three days.

• Soaking through a pad or tampon in an hour or two, repeatedly.

• Needing to wear a pad and a tampon together.

• Waking at night to change protection or finding blood on the bedding.

• Passing clots bigger than a 10p coin.

• Avoiding exercise, travel or work on the heaviest days.

The NHS says heavy periods can be normal at certain times, such as when periods first start, after pregnancy or when approaching menopause. Patient.info adds that heavy periods are more common in the first few years after periods begin and in the months before menopause, when periods are often irregular as well, and that heavy periods in teenagers have a good chance of settling over a few years.

Sometimes a cause is found. The NHS lists conditions affecting the womb or ovaries, including polyendocrine metabolic ovarian syndrome (PMOS), fibroids, endometriosis, adenomyosis and pelvic inflammatory disease; conditions that make you bleed more easily, such as von Willebrand disease; and some medicines, including some anticoagulants and chemotherapy medicines. Patient.info also names womb polyps, an underactive thyroid and a copper coil as possible contributors.

The NHS notes that, rarely, heavy periods can be a sign of womb cancer, which is one reason bleeding between periods or after sex, or a persistent change in your usual pattern, should always be mentioned to a GP.

The NHS advises seeing a GP if heavy periods are affecting your life, if you have had them for some time, if you have severe pain during periods, if you bleed between periods or after sex, or if heavy periods come with other symptoms such as pain when peeing, pooing or having sex.

Patient.info suggests discussing it with a doctor when periods have changed and become heavier than before, usually after three or four periods in a row have changed, and seeking help promptly if you feel unusually tired, faint or dizzy or look pale, because the bleeding may be heavy enough to cause anaemia.

Neither source lists flooding as a reason to call 999 on its own. If you feel faint, collapse, have chest pain or are struggling to breathe, or if you are pregnant or could be pregnant and are bleeding heavily, treat that as urgent and use NHS 111 or emergency services as appropriate. A period diary of the number of products used each day and the days of bleeding, which Patient.info recommends, helps the doctor see how severe things are and whether treatment is working.

According to Patient.info, a doctor may want to do an internal examination to assess the cervix and the size and shape of the womb, although this is not always needed, particularly in younger women without other symptoms. A blood test for anaemia may be done, and blood tests may also check for an underactive thyroid or a bleeding disorder if either is suspected.

Further tests are more likely if there is bleeding between periods or irregular bleeding, bleeding or pain after sex, pelvic pain apart from normal period pain, severe period pain, vaginal discharge or a persistent change in the usual pattern. These can include an ultrasound scan of the womb, swabs for infection, a sample of the womb lining (endometrial biopsy) and hysteroscopy, in which a thin telescope is passed through the cervix to look inside the womb.

The NHS says that if first-line treatments do not work, or a GP thinks a condition may be causing the bleeding, you will usually be referred for tests or to a specialist.

The NHS stresses that heavy periods do not always need treatment, but that treatments can help if they affect your daily life. Treatments from a GP include some types of contraception, such as an intrauterine system (IUS) or the combined contraceptive pill, medicine to reduce bleeding such as tranexamic acid, and prescription anti-inflammatory painkillers such as mefenamic acid or naproxen.

Patient.info gives more detail. It says the levonorgestrel intrauterine system usually works very well, with bleeding becoming very light or stopping within 3 to 6 months in most women. Tranexamic acid can reduce the heaviness of bleeding by almost half in most cases, although it does not shorten the number of days or ease pain. Anti-inflammatory painkillers reduce loss by about a quarter and ease pain, and the combined pill reduces bleeding by at least a third in most women. Many women use tranexamic acid and an anti-inflammatory together because they work in different ways.

Patient.info also describes a short course of a progestogen tablet, such as norethisterone or medroxyprogesterone, as an emergency measure to stop very heavy bleeding, with bleeding usually stopping within 24 to 48 hours of starting. Surgical options include endometrial ablation, removal of fibroids and hysterectomy, which the NHS lists as specialist treatments.

In the UK, most people begin with a GP or a sexual health or contraception service, where first-line medicines and coils can often be started without hospital referral. Specialist gynaecology assessment, scans and procedures such as hysteroscopy or ablation are available through the NHS after referral, and some people choose to arrange these privately. The principles of assessment and the treatment options are the same; the difference is mainly in how quickly appointments are available and who pays.