Passing Blood Clots With Fibroids: When It’s Normal And When To Worry

Passing blood clots during your period is one of the most alarming fibroid symptoms — and one that is rarely explained clearly. This article covers the mechanism, what size and frequency are concerning, and what to do.

Why Fibroids Cause Clots

Blood clots form when blood pools in the uterine cavity before it can be fully expelled. Normally, the uterus contracts rhythmically to expel blood quickly enough that anticoagulants in the endometrial lining prevent clotting. Fibroids disrupt this process in two ways: they increase the volume of blood produced (more to expel) and they disrupt the uterine contractions that move blood through efficiently. When blood pools — particularly in areas of the cavity where fibroid tissue creates irregular contours — it has time to clot before being expelled.

Small Clots Are Common

Small clots — roughly the size of a raisin or smaller — during heavy flow are common and do not by themselves indicate a serious problem. They are unpleasant and alarming, but physiologically they are a consequence of the heavy flow rather than a separate concerning sign.

When To Be Concerned

Large clots consistently: Clots larger than a 50p coin (approximately 2.5cm) or golf-ball-sized clots passing regularly indicate significant menorrhagia that warrants medical assessment. Not because the clots themselves are dangerous, but because the blood loss producing them is substantial enough to cause iron deficiency and potentially anaemia over time.

Clots accompanied by severe pain: Passing large clots with severe cramping — more intense than your usual period pain — is worth discussing with your doctor, particularly if it is a new pattern.

Any bleeding outside your period: Clots or bleeding between periods, after sex, or after menopause always warrant medical investigation regardless of fibroid history.

What Reduces Clotting

NSAIDs from day 1 of your period: Reducing prostaglandins reduces the inflammation that contributes to heavy flow and therefore reduces the conditions that produce clots. See our ibuprofen guide. Tranexamic acid: A prescription non-hormonal medication that specifically reduces blood loss per period by inhibiting fibrinolysis — consistently reduces both flow volume and clot passage. Worth discussing with your GP. Iron management: Address the iron depletion that heavy clotting causes — see our iron deficiency guide. For the full range of medical options for heavy bleeding, see our article on heavy bleeding from fibroids.