Why Is My Period So Heavy? 9 Real Causes + What Helps
Soaking through a pad every hour is not normal. Here are the 9 causes of heavy periods and what actually helps each one.
Blood Clots During Period: When Are They Normal?
Seeing a blood clot in the toilet or on your pad can be alarming — but for most women, small clots on heavy flow days are completely normal. The question is: how big is too big, and when do clots signal something that deserves a doctor visit?
This guide cuts through the confusion with a simple size rule, explains exactly why clots form, and lists the five conditions that cause abnormally large or frequent clotting.
Quick answer
Period clots up to 2.5cm (the size of a quarter coin) are normal, especially on the first two heavy-flow days. Clots larger than a quarter, or heavy clotting on most days of your period, can indicate fibroids, adenomyosis, or a hormone imbalance — and should be investigated.
2.5cm
max normal clot size (quarter coin)
Days 1–2
when clots are most common
1 in 5
women experience heavy menstrual bleeding
Why Period Clots Form
Your uterine lining sheds during your period as a mix of blood, endometrial tissue, mucus, and cervical fluid. To keep this flow moving, your body releases natural anticoagulants — mainly a protein called plasmin — that break down clots before they leave the body.
On light-to-moderate flow days, plasmin keeps pace and blood flows freely. But on your heaviest days — usually days 1 and 2 of your period — the flow outpaces the anticoagulants. Blood pools briefly in the uterus or vagina, clots slightly, and exits as a dark, jelly-like clump. This is normal physiology, not a sign that something is wrong.
The clots you see on heavy days are essentially the same as the clots you'd see if you left blood sitting in a bowl — the difference is just timing and volume.
Normal vs. Not Normal — The Size Guide
Size is the most reliable rule of thumb. Here's a simple visual:
Small
Under 2cm
Normal
Under 2cm
Quarter-sized
~2.5cm
Upper limit
~2.5cm
Larger than a quarter
Over 2.5cm regularly
See a doctor
Over 2.5cm regularly
Normal clots
- Smaller than a quarter coin
- Dark red or dark brown colour
- Appear on your 1–2 heaviest days only
- No severe pain beyond typical cramping
- Flow manageable with a pad or tampon
See a doctor if
- Clots are consistently larger than a quarter
- Clots appear on most days of your period
- Soaking through a pad every hour for 2+ hours
- Clots with severe pain, fever, or foul smell
- Clots after a positive pregnancy test
5 Causes of Abnormally Large Period Clots
If you're regularly passing clots larger than a quarter — especially alongside heavier-than-usual bleeding — one of these five conditions is usually responsible.
Uterine fibroids
Fibroids are non-cancerous muscle growths in or on the uterus wall. Submucosal fibroids — those that push into the uterine cavity — interfere with the uterine lining's ability to shed evenly and suppress the anticoagulants that prevent clotting. They affect up to 70% of women by age 50 and are the most common cause of large period clots. Diagnosis is via pelvic ultrasound.
Adenomyosis
In adenomyosis, the uterine lining grows into the muscle wall itself. This makes the uterus larger, the lining thicker, and periods much heavier — with significant clotting. It is common in women in their 30s and 40s and often causes deep, crampy pain alongside heavy flow. Diagnosis can be difficult; MRI is more reliable than ultrasound for this condition.
Hormonal imbalance (estrogen dominance)
Progesterone thins the uterine lining throughout the second half of your cycle. When progesterone is low relative to estrogen — due to anovulatory cycles, PCOS, or perimenopause — the lining builds up thicker than usual. A thicker lining means more tissue to shed, which means heavier flow and more clotting. A blood test on day 21 of your cycle checks progesterone levels.
Endometriosis
When endometrial tissue grows outside the uterus, it still responds to hormonal cycles — bleeding and inflaming each month with nowhere to go. This drives chronic inflammation in the pelvis, which can worsen uterine bleeding and cause heavier-than-normal periods with clots. Endometriosis affects around 1 in 10 women and is frequently diagnosed late — an average of 7–10 years after symptoms begin.
Bleeding disorders
Conditions such as von Willebrand disease (which affects about 1% of the population) impair the blood's normal clotting cascade. Paradoxically, this can result in heavier menstrual bleeding and more visible clots, because the body cannot efficiently form and break down clots in the normal way. A haematology referral and specific clotting factor tests are needed for diagnosis — it is frequently missed in women whose primary complaint is heavy periods.
When to See a Doctor — and When to Go to the ER
Go to the ER immediately if
- Soaking through a pad or tampon every 15–30 minutes for two hours or more
- Passing large clots continuously and feeling dizzy, faint, or short of breath
- Experiencing severe pelvic pain alongside heavy clotting and fever above 38°C
- You had a positive pregnancy test and are now passing large clots or grey tissue
For anything less acute, book a GP or gynaecology appointment if:
- You regularly pass clots larger than a quarter coin for more than 2 cycles
- Your period has become noticeably heavier than it used to be
- You are experiencing fatigue or shortness of breath (possible iron-deficiency anaemia from blood loss)
- Clots come with worsening period pain year on year
At the appointment, your doctor will likely order a pelvic ultrasound to check for fibroids or adenomyosis, a full blood count to check for anaemia, and possibly a day-21 progesterone test and thyroid panel. If a bleeding disorder is suspected, you'll be referred to haematology for clotting factor tests.
Track your flow with Wamiga
Log heaviness, clots, and pain daily so you have real data to bring to your doctor — not just a guess.
