Uterine Fibroids: The most common cause of heavy menstrual bleeding in women of reproductive age, especially in the 40s. Fibroids can cause heavy, prolonged, or irregular menstrual bleeding due to their location, size, and number.

Hormonal Imbalance: Conditions like polycystic ovary syndrome (PCOS), thyroid disorders, or hyperplasia can lead to hormonal imbalances that affect menstrual cycle regularity and heaviness.
Adenomyosis: A condition where tissue similar to the lining inside the uterus grows into the muscular walls of the uterus, leading to heavy and painful periods.
Endometrial Hyperplasia: Thickening of the uterine lining that can cause heavy or irregular menstrual bleeding, often associated with anovulatory cycles or unopposed estrogen exposure.
Intrauterine Devices (IUDs): Certain types of IUDs, especially those without hormones, can cause heavier menstrual bleeding as a side effect.

Cancer (Endometrial or Cervical): Although less common, cancer of the uterus or cervix can present with abnormal vaginal bleeding, including heavy menstrual bleeding. Early detection is crucial for effective treatment.
Bleeding Disorders: Conditions like von Willebrand disease can lead to heavy menstrual bleeding due to impaired blood clotting.
Pregnancy Complications: Ectopic pregnancy or miscarriage can cause heavy vaginal bleeding and must be considered, especially if there's a possibility of pregnancy.

Uterine Arteriovenous Malformations: Rare vascular anomalies within the uterus that can cause heavy, life-threatening bleeding.
Uterine Sarcomas: Malignant tumors of the uterine muscle or supporting tissues, which are rare but can present with abnormal uterine bleeding.
Systemic Diseases: Certain systemic diseases, such as liver or kidney disease, can affect coagulation and lead to heavy menstrual bleeding, though these are less common causes.