Clots in period blood: what is normal, causes and when to see a GP

Patient.info describes menstrual clots as thick clumps formed from a mixture of blood cells, tissue from the lining of the womb and proteins from the blood. A spokesperson for the Royal College of Obstetricians and Gynaecologists (RCOG) told Patient.info that when you are bleeding heavily, blood pools inside the vagina and clots, much as it would if you were bleeding elsewhere, which is why clots appear typically during the heavier days.

What counts as normal varies from person to person. Patient.info says the key is knowing what is normal for you, and that you only need to contact your doctor about clots if you are worried about them in any way or if they change significantly, for example suddenly becoming much bigger or more frequent.

Small clots, particularly early in a period when flow is heaviest, are common. The NHS explains that many women have heavy periods, that they may be normal for you, and that periods can sometimes be heavy at different times such as when you first start your periods, after pregnancy or approaching the menopause.

The NHS lists signs that suggest heavy periods, which include passing blood clots larger than about 2.5cm, the size of a 10p coin. Leeds Teaching Hospitals describes clots varying in size from a 10p piece to larger than your palm among the features of heavy bleeding, along with bleeding for more than seven days, flooding that needs tampons or pads changed every hour, accidents such as bleeding through clothes or bed sheets, severe tiredness, being told you have anaemia, and bleeding that affects work or daily life.

A single large clot in an otherwise ordinary period is rarely a concern. A pattern of large clots with heavy flow, or a clear change from your usual pattern, is what deserves attention.

The NHS says that heavy periods can sometimes be caused by conditions affecting the womb or ovaries, such as fibroids, endometriosis, adenomyosis, pelvic inflammatory disease and the ovarian condition it names polyendocrine metabolic ovarian syndrome (PMOS), by conditions that make you bleed more easily such as Von Willebrand disease, and by some medicines and treatments including some anticoagulant medicines and chemotherapy. It adds that rarely heavy periods can be a sign of womb cancer.

Leeds Teaching Hospitals lists a similar set and adds endometrial polyps, the copper coil, chronic pelvic infections, hormonal problems such as when an egg is not released in a cycle, as often happens in polycystic ovary syndrome, and an underactive thyroid, as well as blood clotting disorders and medicines that thin the blood. It says that in about half of people with heavy periods, the womb and ovaries are normal, and that this pattern is more common in the first few years after periods start and close to the menopause. Patient.info quotes the RCOG spokesperson as saying that for about 70% of women there is no underlying cause for heavier bleeding and bigger or more frequent clots, and that womb cancer is very rare before the menopause.

Patient.info also notes that unscheduled heavy bleeding and clotting when you are not expecting a period could signal a very early miscarriage, and that if you usually have regular periods and suddenly have a heavy unscheduled bleed, you should take a pregnancy test.

The NHS says to see a GP if heavy periods are affecting your life, you have had heavy periods for some time, you have severe pain during your periods, you bleed between periods or after sex, or you have heavy periods and other symptoms such as pain when peeing, pooing or having sex. The RCOG spokesperson quoted by Patient.info suggests that having to change your sanitary product every hour or two, needing to wear pads and tampons together or clots larger than a 10p piece suggest your period has got a lot heavier than normal and may mean you need to see your doctor.

Heavy bleeding can cause iron deficiency anaemia. Leeds Teaching Hospitals lists severe tiredness and feeling drained during a period and having been told you have anaemia among signs of heavy periods, and says blood tests are used to check for anaemia. If heavy bleeding makes you feel faint or very unwell, seek prompt medical advice, and tell the clinician if you could be pregnant.

Leeds Teaching Hospitals says investigations start with a discussion about your periods, including bleeding after sex or between periods, medicines, past medical problems and family history, and you may be offered an examination of the abdomen and an internal vaginal examination with a chaperone, and swabs for infection. Other tests depend on the assessment: blood tests to check for anaemia, thyroid function and normal blood clotting, an internal ultrasound scan of the pelvis to check for polyps, fibroids and the thickness of the womb lining, and a hysteroscopy, a camera examination of the womb lining with a biopsy, usually in an outpatient clinic.

The NHS adds that you may have a series of blood tests to check if you have underlying conditions such as iron deficiency anaemia, and that if treatments do not work or a GP thinks a condition may be causing heavy periods, they will usually refer you for tests or to see a specialist. Leeds Teaching Hospitals says it is not necessary to measure blood loss before starting any treatment.

The NHS says heavy periods do not always need to be treated, but treatments are available if they are affecting daily life. From a GP these include some types of contraception, such as an intrauterine system (IUS) or the combined contraceptive pill, medicine to reduce the bleeding such as tranexamic acid, and prescription-only anti-inflammatory painkillers such as mefenamic acid or naproxen. Specialist treatments include removing the lining of the womb (endometrial ablation), removing fibroids if they are thought to be the cause, and total or partial removal of the womb (hysterectomy).

Leeds Teaching Hospitals describes the levonorgestrel intrauterine system as working mainly by making the womb lining very thin, so that bleeding becomes very light in most users and in some stops within six months, and says tranexamic acid tablets can reduce the heaviness of bleeding by almost half for most users by strengthening the blood clots in the womb lining. It also says you do not need treatment if you are reassured by normal test results and able to cope with the bleeding, and that eating a healthy unprocessed diet reduces the chance of becoming anaemic.

Heavy bleeding can interfere with work, exercise and sleep. The NHS lists avoiding daily activities such as exercise or taking time off work because of periods among the signs of heavy periods, which is why treatment is offered when it affects quality of life. A symptom diary recording how often you change products, clot size and any pain gives a GP something concrete to work with.

If you are using hormonal contraception, Patient.info notes that the pill taken for several packs back to back followed by a break can cause a heavier withdrawal bleed with more clots, or sometimes the opposite, and that what is normal depends on many variables including weight, hormones and where you are in your cycle.

On the NHS, a GP can start treatment and arrange blood tests and an ultrasound scan, with referral to gynaecology if treatments do not work or an underlying condition is suspected. Private gynaecology consultations offer quicker access to ultrasound and hysteroscopy. Whichever route you use, ask which tests have been done, whether iron levels have been checked and what the plan is if the first treatment does not help.