Blood clots during your period

Blood clots during heavy periods: causes & recommendations  

Passing blood clots during your period can be perfectly normal. The amount, duration and frequency of menstrual bleeding vary from month to month and from woman to woman.

Large blood clots may, however, be a sign that something isn't quite right. If your period seems heavier than usual – for instance, if you're passing very large blood clots – it's worth seeing a specialist.

What are blood clots during menstruation?

Blood clots are one of the body's natural protective mechanisms. The thick, gel-like consistency of a menstrual clot helps prevent the loss of excessive amounts of blood.

Clots form through the very same clotting process that kicks in anywhere else in the body when tissue is injured – after a cut or a graze, for example.

Menstrual clots usually appear when bleeding is heavy. They're most common during the first two days of your period. They may be bright red or a darker, deeper red. Larger clots can look almost black. Towards the end of your period, the blood appears darker and browner, because it's older and leaves the body more slowly.

Blood clots during menstruation – how do they form?

Clots form when the womb lining sheds larger amounts of blood. When blood collects in the womb or the vagina (which we've covered in detail in our article All about the vagina), it starts to clot, just as it would on an open skin wound. The consistency of menstrual blood changes both over the course of your period and from cycle to cycle. One month you might have heavy bleeding with menstrual clots, the next a lighter flow with none at all. These fluctuations are entirely natural. Changes can also be influenced by diet and lifestyle.

Normal vs. unusual blood clots during menstruation

If the clots are small and only appear occasionally, there's generally no cause for concern. Unlike blood clots in the veins, menstrual clots themselves aren't dangerous.

Normal clots:

• are smaller than a coin
• appear only occasionally, usually at the start of your period
• are bright red or dark red

Large clots that appear regularly during your period may point to an underlying condition that should be investigated – particularly if they occur month after month.

Large blood clots during menstruation

Every woman's period is different, and passing the occasional blood clot is perfectly normal. HERE we've summarised everything worth knowing about the menstrual cycle and period symptoms.

If the clots are very large and the bleeding very heavy, however, this may be a sign of a more serious condition. The most common causes are:

• Uterine fibroids. Various types of fibroid can affect bleeding and cause clots, though most often it's a fibroid growing into the uterine cavity (a submucosal fibroid).
• Your method of contraception. It isn't only the pill that can affect your cycle. Even a hormone-free coil can cause large clots and heavier bleeding than usual.
• Miscarriage. An early miscarriage or an ectopic pregnancy can cause heavy blood loss that may be mistaken for an enormous clot.
• Endometriosis. Alongside severe cramping and abdominal pain, large clots can be another sign of endometriosis.
• Polycystic ovary syndrome. This is a common cause of hormonal disturbances and irregular periods with large clots.
• Other chronic conditions. Von Willebrand disease, sexually transmitted infections and pelvic inflammatory disease are further possible causes.

Heavy periods with clots

A period is considered heavy when the body either sheds very large amounts of menstrual blood or the bleeding continues over a prolonged period.

If, for example, you need to change your tampon or pad every one to two hours, or you need two types of menstrual protection at once (a tampon plus a pad, say), this may indicate a heavy period. A period with clots that lasts longer than seven days is also considered heavy.

If it's always been this way and there are no worrying symptoms such as ovarian pain, abdominal cramps or fever, this may simply be normal for you. But if the bleeding interferes with your daily life, or if these changes come on suddenly, you should have your symptoms assessed by a doctor so that appropriate treatment can be found.

Periods with pieces of tissue

Normally the body sheds small particles of tissue, blood and secretions along with menstrual blood.

More rarely, a so-called decidual cast (membranous dysmenorrhoea) occurs, in which the womb lining no longer breaks down to be shed gradually. Instead it is passed in a single large piece, retaining the shape of the womb. It consists of endometrium, blood and secretions, and is characterised by:

• a size roughly equivalent to the palm of a hand
• the shape of an inverted triangle, similar to the womb
• an appearance like a piece of red meat, or like a very large version of a menstrual clot

This is an extremely rare phenomenon, described fewer than 25 times in the medical literature. Observations to date don't suggest that a decidual cast conceals other health problems. In most cases the pain subsides shortly after the lining is passed.

Menstrual clots with membranous pieces

Menstrual flow consists of a wide range of different tissues, dead cells and clotted blood. As a result, broken-down particles of womb tissue can appear as blood clots with membrane-like, gelatinous parts.

These "membranes" in menstrual blood are usually entirely normal, no cause for concern and require no medical treatment. They should, however, be assessed by a doctor if other symptoms accompany them.

An unusual consistency of menstrual blood, changes in the heaviness of bleeding or severe lower abdominal pain can point to conditions such as endometriosis or infections of the reproductive system.

When should you see a doctor?

See your doctor if you have very heavy menstrual bleeding or larger clots than usual. Menstrual bleeding is considered heavy if you need to change your tampon or pad every two hours or more often over the course of a day.

Not all bleeding during pregnancy is a cause for concern. It may be harmless – in another article you can read all about bleeding in pregnancy. Clots, on the other hand, can be a sign of miscarriage; in that case immediate medical assessment is essential.

Causes – why do blood clots form during menstruation?

Most women of childbearing age shed the womb lining every 28 to 35 days. This lining is also known as the endometrium. As it is shed, it mixes with:

• blood
• blood breakdown products
• mucus
• tissue

This mixture is then carried out of the womb through the cervix and out of the vagina. As the womb lining detaches, it collects in the lower part of the womb, waiting for the cervix to contract and expel the contents. To break down this thickened blood and tissue, the body releases anticoagulants that liquefy the material and allow it to pass more easily. If the volume of blood exceeds the body's ability to produce anticoagulants, menstrual clots form and are passed during your period.

Physical and hormonal factors can affect your cycle and lead to heavy bleeding. Heavy bleeding increases the likelihood that menstrual clots will form.

Hormonal disturbances

For the womb lining to build up and thicken properly, a hormonal balance of oestrogen and progesterone is required. If there's too much or too little of either, heavy menstrual bleeding can result. 

A hormonal imbalance may be caused by:

• perimenopause
• menopause
• stress
• significant weight gain or loss

The main symptom of a hormonal imbalance is an irregular period. It might start later or earlier, last longer, or skip a month altogether. On the Enroush blog we've discussed the symptoms and types of hormonal disorders in more detail HERE.

Endometriosis

Endometriosis is a condition in which cells similar to those of the womb lining – known as endometrial cells – grow outside the womb and within the genital tract. Around the time of your period, this condition can cause a range of uncomfortable symptoms, including painful, heavy bleeding that may contain blood clots.
The exact cause of endometriosis is unknown, but heredity, hormones and previous pelvic surgery are all thought to play a role. Find out more about endometriosis on our blog!

Fibroids or polyps

Uterine fibroids and polyps are usually benign muscular growths that develop in the wall of the womb. As well as heavy menstrual bleeding, they can cause irregular periods and so lead to the formation of blood clots.

Enlarged womb

After pregnancy, the womb often remains somewhat larger than before. An enlarged womb can also result from structural changes such as fibroids. This creates additional space in which blood can collect, which can lead to increased clotting and the appearance of clots during menstruation.

Uterine fibroid (myoma) 

Uterine polyps and fibroids affect around 70% of women and can frequently cause heavy periods with clots. Although they aren't malignant, they can interfere with the normal contractions of the womb. If the womb doesn't contract properly, blood isn't expelled as easily but more slowly – which is why it can clot during this time.

Fibroids that develop within the muscular tissue of the womb wall can also cause other symptoms. These include persistent lower back pain, spotting, dyspareunia (pain during intercourse), a feeling of bloating and fertility problems.

Pregnancy loss

With a miscarriage or pregnancy loss, a woman will usually pass several large clots – depending on the stage of pregnancy. Pregnancy loss can sometimes occur before a woman even knows she's pregnant, so an early miscarriage may be mistaken for an ordinary period.

Cancer

Although rare, malignant tumours of the womb and cervix can lead to heavy menstrual bleeding and large blood clots.

Adenomyosis

Adenomyosis occurs when the womb lining grows into the wall of the womb, for reasons that aren't fully understood. This causes the womb to enlarge and thicken. As well as prolonged and heavy bleeding, this common condition can cause the womb to grow to two or three times its normal size. Menstrual clots are common in those affected.

Blood clotting disorders

Some haematological conditions can be responsible for heavy menstrual bleeding, because they affect the clotting proteins the womb lining needs to stop the bleeding. Conditions such as platelet function disorders or von Willebrand disease (VWD) can cause unusually heavy bleeding with blood clots.

Iron deficiency associated with iron-deficiency anaemia, and vitamin and mineral deficiencies

A lack of certain vitamins and minerals, particularly iron, can lead to the formation of blood clots during menstruation.

Iron deficiency is the leading cause of anaemia – specifically iron-deficiency anaemia – and can interfere with the body's natural clotting process. This form of anaemia can also cause menorrhagia, that is, heavy bleeding over prolonged periods.

Women in this situation are often advised to take an iron supplement to replenish the body's stores. Other vitamins that contribute to the formation of red blood cells include vitamin C, folic acid and vitamin B12. If there are multiple deficiencies, your doctor may also recommend taking a multivitamin supplement.

Von Willebrand disease

Von Willebrand disease is a rare, inherited blood disorder. It's caused by a deficiency of von Willebrand factor, which plays a central role in clotting and in the formation of a blood clot. Unusual bleeding is therefore the main symptom of this condition.

The condition can often be recognised easily by heavy blood loss even from minor injuries.

Around 50% of women with von Willebrand disease pass blood clots during their period. The bleeding is very heavy, so a tampon or pad has to be changed every one to two hours. It's one of the few conditions that can cause large blood clots of over 2.5 cm during menstruation.

Polycystic ovary syndrome

Clots during menstruation can also occur in women with polycystic ovary syndrome (PCOS). As well as the reproductive system, PCOS affects metabolism and the vascular system. A common symptom is heavy bleeding, caused by the follicles developing in the ovaries not releasing eggs regularly.

When this happens, the body can't produce anticoagulants quickly enough to keep pace with the large volume of blood and prevent clotting. This is why large blood clots may be passed during menstruation.

Irregular periods with severe pain are another common symptom of polycystic ovary syndrome.

Pelvic inflammatory disease

Pelvic inflammatory disease (PID) is an infection of the upper genital tract that usually begins in the vagina and spreads upwards into the womb, fallopian tubes and ovaries. It can significantly affect menstruation, and the inflammation may be accompanied by pain, fever and unusual discharge. HERE we've discussed the causes and types of vaginal discharge in more detail.

PID can also be responsible for unusual bleeding and periods with black blood clots. It's important to see a specialist as soon as possible if you notice persistent black clots or if other symptoms suggesting health problems appear alongside them.

Side effects of certain medicines and hormone therapies

If a woman notices she's passing very large clots during her period, it's worth reviewing any medication taken recently as well as any long-term treatments. The body may be reacting with a side effect, and the treatment may need to be stopped or the medication adjusted.

Hormone therapies containing oestrogen and progestin, anti-inflammatory medicines and anticoagulants are just some of the factors that can affect how heavy your bleeding is and your usual cycle. Thyroid medication and chemotherapy as part of cancer treatment can also alter menstruation. Any side effects should be discussed with your specialist without delay.

Diagnosis

To determine the underlying cause of menstrual clots, your gynaecologist will ask you a series of questions about factors that affect menstruation. You might be asked whether you've had previous pelvic surgery, whether you use contraception, or whether you've ever been pregnant. The womb will also be examined for any changes.

Blood tests may also be recommended to identify hormonal imbalances. Imaging such as an MRI scan or ultrasound can be used to detect fibroids, endometriosis or other obstructions.

Treating blood clots during menstruation

Depending on the underlying cause of the blood clots, your specialist may recommend various treatments – surgical, medical or hormonal. 

Surgical treatment

Sometimes surgery may be necessary to treat significant blood clots during menstruation.

Dilatation and curettage (a D&C) can be used both to establish the cause of heavy menstrual bleeding and to treat various conditions. The cervix is dilated and the womb lining removed. The procedure is usually carried out as a day case under sedation. Although it won't permanently resolve heavy bleeding, it provides relief for a few months until the lining thickens again.

For women with uterine growths such as fibroids that don't respond well to medical treatment, surgery to remove them may be necessary. The type of procedure depends on the size and location of the growths. For large fibroids and uterine polyps, a myomectomy is performed. This involves a larger abdominal incision to gain access to the womb.

If the growth is small, laparoscopic surgery is often possible. Laparoscopy involves small incisions in the abdomen, which can shorten recovery time. Some women opt to have the womb removed. This procedure is called a hysterectomy.

Medical treatment

Doctors may recommend taking non-steroidal anti-inflammatory drugs during your period to relieve symptoms such as cramps, pain and discomfort. They can also help with excessive bleeding.

If you'd rather not use hormonal treatments, you might consider medicines that affect blood clotting. The most commonly recommended medication of this type is tranexamic acid.

Hormone therapy

Hormonal contraceptives can inhibit the build-up of the womb lining. A hormone-releasing coil can reduce the volume of bleeding by up to 90%, and the contraceptive pill by around 50%. Hormonal contraceptives can also help slow the growth of fibroids and other adhesions in the womb. Find out more about coils and contraceptive pills on our blog.

Treatment alternatives and prevention

A period with small, occasional clots is harmless and requires no treatment. It's normal for the body to sometimes pass menstrual blood with a gel-like consistency, particularly when it has remained in the body for longer.

Some helpful tips to avoid the formation of such clots:

• Drink enough and stay well hydrated
• Meet your daily requirements for vitamins and minerals, especially iron, vitamin C, vitamin D and vitamin B12
• Lead an active lifestyle with regular physical exercise
• Limit foods high in vitamin K, as this vitamin promotes clotting
• Use stress management techniques
• Get plenty of rest and sleep

If, on the other hand, the clots are accompanied by pain, heavy bleeding, bleeding between periods or other uncomfortable symptoms, they should be assessed by a specialist so the cause can be treated.

Complications – periods with clots

Menorrhagia is the medical term for unusually heavy or prolonged menstrual bleeding. With this condition, the cramping and heavy bleeding during your period may prevent you from going about your usual daily activities.

See your doctor if you regularly pass large clots. One of the most significant complications of heavy menstrual bleeding is iron-deficiency anaemia. Anaemia occurs when there isn't enough iron in the blood to form healthy red blood cells. Symptoms include:

• fatigue
• weakness
• pallor
• shortness of breath
• chest pain

Questions and answers

Still have questions about blood clots? You'll find the answers here!

Are blood clots a warning sign?

In most cases, blood clots are not a warning sign. As long as they appear only occasionally and are small – roughly the size of a coin – they're a normal part of your period.

Is it normal for menstrual blood to have a thicker consistency?

Menstrual blood can sometimes have a thicker consistency and a darker colour, especially towards the end of your period. If you notice that it's thicker every month, however, you should have blood tests done to check whether your blood count is within the normal range.

References:

1. Observations on the clotting of menstrual blood and clot formation - https://www.sciencedirect.com/science/article/abs/pii/0002937871904704

2. Blood Clots During Menstruation: A Concern? - https://www.mayoclinic.org/diseases-conditions/menorrhagia/expert-answers/blood-clots-during-menstruation/faq-20058401

3. Are blood clots normal during a period? - https://www.medicalnewstoday.com/articles/322707

4. Period Blood Clots: Should You Be Concerned? - https://health.clevelandclinic.org/period-blood-clots-are-they-normal

5. Heavy Periods - https://www.nhs.uk/conditions/heavy-periods/

6. What Do Blood Clots During Your Period Mean? - https://www.health.com/blood-clots-during-a-period-8563877

7. Period Blood Clots: Cause for Concern? - https://www.verywellhealth.com/why-are-there-blood-clots-in-my-period-2721935

8. Blood clots during your period - what are they? - https://helloclue.com/articles/cycle-a-z/blood-clots-during-your-period-what-are-they

9. Medicines That Can Cause Changes in Menstrual Bleeding - https://myhealth.alberta.ca/Health/pages/conditions.aspx?Hwid=tv7209

10. Von Willebrand Disease - https://www.mayoclinic.org/diseases-conditions/von-willebrand-disease/symptoms-causes/syc-20354978

11. What Is a Decidual Cast? - https://www.verywellhealth.com/what-is-a-decidual-cast-7152647