Anovulatory cycles: This is a common cause of heavy menstrual bleeding in adolescents, especially in the first few years after menarche. The immature hypothalamic-pituitary-ovarian axis can lead to irregular ovulation, resulting in anovulatory cycles and subsequent heavy bleeding.

Immature uterine bleeding: Similar to anovulatory cycles, this condition is related to the immaturity of the hypothalamic-pituitary-ovarian axis and can cause heavy menstrual bleeding.
Hormonal imbalance: Fluctuations in estrogen and progesterone levels can lead to heavy menstrual bleeding.
Bleeding disorders: Conditions such as von Willebrand disease or platelet function disorders can cause heavy menstrual bleeding due to impaired coagulation.

Pregnancy complications: Although the patient reports regular periods, it's essential to rule out pregnancy-related complications, such as a molar pregnancy or ectopic pregnancy, which can cause heavy bleeding.
Uterine anomalies: Congenital uterine anomalies, such as a unicornuate uterus, can increase the risk of heavy menstrual bleeding.
Thyroid disorders: Both hypothyroidism and hyperthyroidism can cause menstrual irregularities, including heavy bleeding.
Coagulopathy: Conditions such as thrombocytopenia or clotting factor deficiencies can lead to heavy menstrual bleeding.

Uterine fibroids: Although rare in adolescents, uterine fibroids can cause heavy menstrual bleeding.
Adenomyosis: A condition characterized by the growth of endometrial tissue into the uterine wall, which can cause heavy bleeding.
Pelvic inflammatory disease: A rare cause of heavy menstrual bleeding in adolescents, often associated with sexually transmitted infections.
Bleeding due to malignancy: Extremely rare, but it's essential to consider the possibility of a malignant tumor, such as a uterine sarcoma, causing heavy menstrual bleeding.