Your Complete Guide to Period Blood Clots

Our bodies are amazing and unique. No two menstrual cycles are ever the same from person to person and, while this in itself is pretty awesome, it can lead to a variety of questions too, especially when it comes to period blood and clots. So, what makes period blood clots, and should you be concerned about them? The WUKA experts have put together a guide to help you understand exactly what is classed as normal period clots, and the reasons why they might occur. Read more here.

What are Period Blood Clots?

Ever noticed thick ‘blobs’ of blood during your period? These are period clots, made up of coagulated blood and tissue. While they might sound alarming, they’re actually completely normal for most women and people with periods. In fact, in most cases, clots are a sign that everything is working as it should.

What Makes Period Blood Clot?

Clots occur when period blood (a mixture of blood, tissue and mucus) builds up inside the uterus, waiting for the cervix to contract and expel it from the body. 

Usually, the body will release anticoagulants to thin the mixture so that it can be passed easily; however, if the body isn’t able to do this quickly enough, the period blood can build up inside the uterus.

Mr. Hemant Vakharia, consultant gynaecologist at London Gynaecology, explains further:

‘Within our blood there are tiny cells called platelets and clotting factors. When a blood vessel is damaged, the platelets gather at the site of the damage and along with clotting factors, they from a clot to stop the bleeding. During a menstrual period, when the womb lining is shed, there is bleeding from the blood vessels in the womb. If the blood accumulates in the womb or vagina it will form a blood clot due to this mechanism.’

Rest assured, this is all quite normal, especially during the first two days of your period when blood flow is heaviest.

blood on towel

What Do Period Blood Clots Look Like?

Menstrual clots can differ in size, consistency and colour. If you’re already tracking your cycle and you know what is normal for you when it comes to your flow (use our guide to period blood colour to check), then you have probably already noticed some clots during your period.

Of course, all bodies are different, so, as a general guide, menstrual clots will generally fall into one of the below categories:

Normal Period Blood Clots

A normal clot will range from bright to dark red in colour and have a thick, almost jelly-like consistency. They are usually no bigger than 2cm in size and will occur mainly during the heaviest days of bleeding. Again, tracking your period helps you to understand your flow and you are likely to know when to expect heavier bleeding.

Brown Blood Clots in Period

Brown clots are nothing to be alarmed about. They may occur towards the end of your period, as the blood flow slows down and therefore takes longer to leave your uterus. The longer the blood takes to leave the body, the darker it becomes.

This is why you might also experience brown clots at the start of your period too. This is simply your body expelling ‘old' blood from your previous cycle.

Small Blood Clots in Period

Small clots are not usually anything to be concerned about and lots of women will experience them during their period. Most normal clots can measure around 2cm in size. As a general guide, the NHS advises that if they are no bigger than a 10p piece, there is usually no cause for concern.

Normal Blood Clots vs Abnormal Blood Clots

While most period clots are completely normal, it is always worth knowing more about abnormal clots and what they could mean for you. It makes sense to be able to spot the differences between what is normal and what could potentially be a symptom of an underlying issue.

Understanding Abnormal Period Blood Clots

The reasons why you may be experiencing abnormal clots can vary, and it is never a good idea to ignore them. If you experience heavy periods, your clots are bigger than 2cm in size, and being passed more than once every couple of hours, this could indicate an issue.

If you are at all worried, we always recommend seeking professional advice from a healthcare provider, so that any underlying issues can be identified.

blood in water

Potential Underlying Causes of Abnormal Blood Clots

Your doctor may run tests to identify possible underlying causes:

Uterine Fibroids

Sometimes, clots can be caused by uterine fibroids. These are common, non-cancerous growths and are usually nothing to be concerned about. Mr. Hemant Vakharia says:

‘Uterine fibroids are known to cause heavy bleeding during periods. As a result, the volume of blood loss is higher than in a normal menstrual period and this blood will form clots. In some cases, they can be large and cause cramps as they are passed through the cervix.’

If you’re concerned about heavy bleeding or clots due to fibroids, speak to your doctor about potential treatments.

Hormone Imbalances

During your cycle, your body relies on a delicate balance of oestrogen and progesterone to keep things ticking over nicely.

Dr. Ghazala Aziz-Scott, specialist in integrative women’s health and biogenetical hormone balancing at Marion Gluck Clinic, sheds more light on how hormones in the body can play a role in the formation of abnormal clots:

‘The lining of the womb and how it sheds depends on the balance of oestrogen and progesterone within the body; oestrogen makes the lining get thicker and progesterone stabilises the lining. Conditions that are linked with high levels of oestrogen can cause heavy, clotty periods. Low progesterone levels also cause heavier bleeding. So, for example, in the perimenopause, women have cycles in which they do not ovulate and this lack of progesterone in the luteal phase causes heavy periods, often with clots such that women can develop anaemia.

'Other hormonal conditions such as hypothyroidism and high cortisol levels associated with stress also impact menstrual flow in this way,' he goes on to say.


Endometriosis is a condition where the uterus lining thickens and starts to grow on other pelvic organs, such as the ovaries or fallopian tubes. It can cause heavy bleeding during your period, and can be another underlying cause of abnormal clots.


Adenonmyosis is a common condition, affecting 1 in every 10 women in the UK (NHS). The most common symptom is heavy periods, resulting from the endometrium (uterus lining) growing into the muscle of the uterus. Often women will also experience irregular periods and pain or discomfort in the pelvis area too. 

Speak to Your Gynaecologist About Abnormal Clotting

Because there are a variety of conditions that could lead to abnormal clotting, it is always a good idea to speak to your gynaecologist so that you can understand what is happening and why. This is especially important if you feel that your everyday life is being negatively impacted by your period and are experiencing a lot of pain with each cycle too.

It is also worth noting that abnormal clotting can lead to other health complications, such as iron deficiency anaemia. Your doctor will help you to decide if treatment is required and may recommend special tests to get a better picture of what’s going on. A heavy period with abnormal clotting is definitely not something you should just live with, so always seek advice.

Use Period Underwear to Manage Blood Clots

One of the biggest complaints from women who experience heavy periods is the need to constantly change sanitary protection – and even to double up with pads and tampons on the heaviest days. Having to change your period protection every 1-2 hours, or bleeding through to your underwear or bedding can really have a negative impact on your daily life – not to mention the financial burden it imposes!

If this sounds familiar, reusable period pants might just be the solution you’re looking for. They eliminate the need for tampons and pads altogether, and many people find they can use them for longer periods of time too.

Our WUKA Super Heavy Period Pants can hold up to 60ml of blood, which is the equivalent of 12 regular tampons and can be worn for up to 10 hours if necessary.

For slightly lighter days, our Heavy Period Pants can be worn for 4-6 hours and hold up to 20ml of blood, roughly 4 tampons’ worth.

super heavy period pants holds up to 60ml of period blood

If you are experiencing clots during your cycle, Super Heavy and Heavy Flow Period Pants can be a real game changer, and can enable you to carry on with your usual activities stress-free. Get in touch you have any questions and we’ll be happy to answer them for you!

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