Period blood clots: what's normal and when to worry

Why period blood clots

Menstrual blood is a mix of blood, uterine lining and mucus. Normally your uterus releases natural anticoagulants that stop it clotting so it can flow out easily. On heavy days, blood can pool in the uterus or vagina faster than those anticoagulants can act, and small clots form. That's why clots are most common on the first one or two days, first thing in the morning after lying down overnight, or when you stand up after sitting for a while.

Clots are usually dark red or almost black and jelly-like. Small bits of lining can look similar. Both are normal in small amounts.

What size is normal?

What causes larger or more frequent clots

Larger clots usually go hand in hand with heavy periods. Anything that makes your flow heavier or slows it leaving the uterus can lead to more clotting:

• Fibroids, which can enlarge the uterus and change how it contracts
• Adenomyosis, where lining-like tissue grows into the uterine muscle
• Polyps in the lining
• Hormone shifts, for example in perimenopause or with irregular ovulation, which let the lining build up more
• Endometriosis
• Bleeding disorders such as von Willebrand disease (often with heavy periods since your first one)
• Miscarriage, which can cause clots and grayish tissue
• After childbirth, when bleeding (lochia) and clots are expected for a while

What helps

• Treat the heavy flow. If clots come with heavy periods, the treatments for heavy bleeding usually reduce clots too: the hormonal IUD, tranexamic acid, NSAIDs on heavy days or hormonal contraception.
• Check your iron. Frequent large clots mean you're losing a lot of blood, so ask for an iron and anemia test.
• Practical comfort: a higher-absorbency pad or period underwear overnight, a towel on the bed, and a slow first stand-up in the morning.
• Write it down. How many clots, how big (compare to a coin) and on which days. Photos can feel awkward, but they help doctors.

What a doctor may check

If you mention large or frequent clots, a doctor will usually ask about how heavy and how long your periods are, check for anemia with a blood test, and may examine you or arrange a pelvic ultrasound to look for fibroids, polyps or adenomyosis. If you've had heavy periods since your very first one, or bleed easily in other ways, they may test for a bleeding disorder. Bringing a few cycles of notes on flow and clots makes this conversation much quicker.

Clots and peace of mind

Seeing a large clot can be frightening, especially the first time. Most of the time, small clots are just part of a heavier day. Knowing what's normal for you, and having a record of your flow, turns a scary moment into a clear question for your doctor. Heavy, clotty periods can also leave you drained and low on the first days of your cycle, so be gentle with yourself on those days. See mood during your period.