Blood Clots During Period: What Is Normal and When to Worry

Blood clots during your period are usually normal, and small, jelly-like clots the size of a dime or a quarter are common on heavy days. Clots larger than about 2.5 cm (about the size of a quarter), or bleeding that soaks a pad or tampon every hour for several hours, can be a sign of heavy menstrual bleeding, and that is worth a talk with a doctor.

This guide explains why clots form, what size and pattern is common, what large clots can mean, and what to write down before an appointment. It is general information and not medical advice.

Why period blood clots form

During a period, the lining of your uterus sheds and small blood vessels bleed. To stop you losing too much blood, your body makes clots from plasma and platelets. When the flow is heavy, blood collects inside the uterus and clots as it sits there.

That is why you often notice a clot when you stand up after you sit or lie down for a while, or when you go to the toilet. To pass a big clot, the cervix has to open a little, and this can hurt. It is part of the reason heavy days with clots often come with cramps.

What normal period clots look like

Most clots are soft and jelly-like. They are often:

• Small. A clot the size of a dime or a quarter can be normal for you.
• Bright red at the start and the end of your period, when the blood moves fast and has no time to darken.
• Dark red or maroon in the first few days, when the flow is at its heaviest.

One heavy day with a few clots in a cycle is less of a concern than heavy clotting that comes back every month. The pattern over time matters more than one bad day.

How many clots are normal?

There is no set number. Doctors look at the size of the clots and how often they come. Clots the size of a quarter or larger that come more than once or twice in a period can be a sign of heavy bleeding. Clots the size of a golf ball that you pass every couple of hours are a problem, so see a doctor.

When clots point to heavy menstrual bleeding

Large clots are one sign of heavy menstrual bleeding (menorrhagia). Heavy bleeding is very common, and treatment can help. Any one of these can be a sign of it:

Heavy periods can be normal at some times, such as when periods first start, after pregnancy or near the menopause. If the heavy bleeding is new for you, or it gets in the way of your life, see a doctor.

What causes large blood clots during a period

Heavy bleeding with large clots has many possible causes. Some of the main ones are:

• Fibroids and polyps. These are growths in or on the uterus. Fibroids are usually not cancer.
• Adenomyosis. Tissue like the lining of the uterus grows into the muscle wall of the uterus. Read more about adenomyosis symptoms and how it differs from endometriosis.
• Endometriosis. It can cause heavy menstrual bleeding as well as pain. See the common symptoms of endometriosis.
• Irregular ovulation. If you do not ovulate regularly, the lining of the uterus can get too thick. This is common in puberty and perimenopause, and with PCOS or an underactive thyroid.
• Bleeding disorders. When the blood does not clot properly, periods can be heavy. See the next section.
• Medicines. Blood thinners, aspirin and the copper IUD can make periods heavier.
• Pregnancy loss. Heavy bleeding can come from a miscarriage or an ectopic pregnancy. If you are pregnant, or you could be, and you pass clots, contact your doctor or go to the nearest emergency room.

Rarely, heavy bleeding is an early sign of cancer of the uterus. This is most often found after the menopause. Sometimes no cause is found.

Could it be a bleeding disorder?

Von Willebrand disease is the most common bleeding disorder. Ask your doctor about a bleeding disorder if you have heavy periods and also:

• Nosebleeds that happen five times or more in a year, or last more than 10 minutes.
• Bruises larger than a quarter that come with little or no injury.
• Heavy or long bleeding after surgery or childbirth.

A blood test can check for clotting problems, and there are medicines that help the blood clot.

Heavy periods with clots and low iron

Blood loss from heavy periods can lead to iron-deficiency anaemia. Heavy periods are a very common cause. Signs of iron deficiency anaemia include:

• tiredness and lack of energy
• shortness of breath
• a heartbeat you can feel (palpitations)
• skin that is paler than usual
• headaches

A full blood count can show if you have it. If you do, the usual treatment is iron tablets for about 6 months, and the doctor also treats the cause. Do not guess at iron. Ask for the test. If you are tired every month, our guide to period fatigue explains the other causes too.

What to track before you see a doctor

A doctor will want details about several cycles: the start date, how long you bled, and how heavy the flow was. A calendar or an app helps you see if your periods are heavier or longer than before.

For each day of your period, note:

• Clots. Yes or no, the size compared with a coin, and how many.
• Pads or tampons. How many you used, and how fast you soaked them.
• Night changes and leaks. Any times you woke to change, or bled through.
• Pain. How bad the cramps were, and if they came with the clots.
• Energy. Tiredness, shortness of breath or feeling faint.
• Other bleeding. Bleeding between periods, nosebleeds or easy bruises.

Also bring a list of your medicines, and say if you could be pregnant. The doctor may do a pelvic exam, a blood test or an ultrasound. Our guide to a pain diary for your doctor shows how to share a record like this.

Endolog is a pain and symptom diary app. You can log flow, clots, pain and tiredness on the same day, so your doctor sees the pattern and you do not have to rely on memory.

Treatment for heavy periods with clots

Heavy periods do not always need treatment. If they affect your life, options include some types of hormonal contraception, anti-inflammatory painkillers and tranexamic acid, a medicine that reduces bleeding. If these do not work, or a condition such as fibroids may be the cause, a doctor can refer you for tests or to a specialist. Your doctor will explain which options suit you.

When to see a doctor

See a doctor if:

• you pass clots larger than about 2.5 cm more than once or twice a period
• heavy periods affect your life, or you have had them for some time
• you have severe pain during your periods
• you bleed between periods or after sex
• you have signs of low iron, such as tiredness and shortness of breath
• your clots or your flow change from what is normal for you

When to get urgent help

Get emergency care if:

• you soak two or more pads or tampons each hour for two to three hours in a row
• you are pregnant, or could be, and you pass clots or bleed heavily
• you bleed heavily and feel faint, dizzy or very short of breath, because a large blood loss can lower your blood pressure and severe anaemia can strain your heart

Frequently asked questions

Are jelly-like clots during a period normal?

Yes, in most cases. Jelly-like clots form when blood collects in the uterus before it leaves. Small ones on your heaviest days are common.

What size of period clot is too big?

Clots larger than about 2.5 cm, the size of a quarter, can be a sign of heavy bleeding, most of all when they come often. Golf-ball-sized clots that come every couple of hours are a problem.

Why do I pass clots when I stand up?

Blood pools in the uterus while you sit or lie down, and it clots as it sits. When you stand up, the clot comes out.

Can endometriosis cause blood clots during a period?

Endometriosis can cause heavy periods, and large clots come with heavy flow. Adenomyosis and fibroids are other common causes. Our page on adenomyosis belly covers the swelling that can come with heavy periods.

This article is for general information. It is not medical advice and does not replace advice from your own doctor. If you think you have an emergency, call 911.