What are common causes of heavy menstrual bleeding?

Heavy menstrual bleeding is most commonly caused by hormonal imbalances, uterine fibroids, endometriosis, thyroid disorders, and blood clotting disorders, according to the American College of Obstetricians and Gynecologists.

Hormonal imbalances represent the leading cause of heavy menstrual bleeding, particularly involving estrogen and progesterone fluctuations. These imbalances can occur during perimenopause, after childbirth, or due to polycystic ovary syndrome (PCOS). When hormone levels are disrupted, the endometrial lining may build up excessively, resulting in heavier bleeding during menstruation.

Uterine fibroids are non-cancerous growths in the uterine wall that affect approximately 70-80% of women by age 50. These benign tumors can significantly increase menstrual flow by enlarging the uterine cavity and interfering with normal muscle contractions that help control bleeding. Fibroids located within the uterine lining (submucosal fibroids) are particularly likely to cause heavy bleeding.

Endometriosis occurs when uterine tissue grows outside the uterus, affecting roughly 10% of reproductive-age women. This condition can cause heavy, prolonged periods accompanied by severe cramping. The displaced tissue continues to thicken and bleed during each menstrual cycle, but cannot exit the body normally.

Thyroid disorders, particularly hypothyroidism, can disrupt normal menstrual patterns. The thyroid gland regulates metabolism and hormone production, so when thyroid function is impaired, it can lead to irregular and heavy menstrual bleeding. Blood tests measuring thyroid-stimulating hormone (TSH) levels can help diagnose these conditions.

Blood clotting disorders, such as von Willebrand disease, affect the body's ability to form proper blood clots. Women with these conditions may experience prolonged, heavy menstrual bleeding because their blood cannot clot effectively to stop the flow. This condition affects approximately 1% of the population but may be underdiagnosed in women.

Other causes include certain medications (particularly blood thinners), intrauterine devices (IUDs), pelvic inflammatory disease, and rarely, uterine or cervical cancer. Birth control pills can sometimes initially cause heavy bleeding before regulating menstrual cycles.

Medical evaluation is recommended when menstrual bleeding soaks through a pad or tampon every hour for several consecutive hours, lasts longer than seven days, or significantly impacts daily activities. Understanding menstrual cycle irregularities can help identify when professional medical assessment becomes necessary.

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