Dysfunctional Uterine Bleeding (DUB): This is the most common cause of abnormal vaginal bleeding in women of reproductive age. It is often related to hormonal changes, particularly anovulatory cycles, which can lead to irregular and heavy bleeding.

Uterine Fibroids: These are common in women of this age group and can cause heavy, prolonged, or irregular menstrual bleeding due to their location, size, and effect on the uterine lining.
Endometrial Hyperplasia: This condition, characterized by the thickening of the uterine lining, can lead to irregular and heavy bleeding. It's more common in women approaching menopause but can occur in younger women, especially those with risk factors like obesity and polycystic ovary syndrome (PCOS).
Intrauterine Device (IUD) Complications: If the patient has an IUD, complications such as malposition or expulsion can cause irregular bleeding.
Thyroid Dysfunction: Both hyperthyroidism and hypothyroidism can affect menstrual regularity and cause abnormal bleeding.

Endometrial Cancer: Although less common, endometrial cancer is a critical diagnosis not to miss. Risk factors include obesity, unopposed estrogen exposure, and certain genetic syndromes. Any postmenopausal bleeding or irregular bleeding in perimenopausal women warrants investigation.
Cervical Cancer: Abnormal vaginal bleeding, especially postcoital bleeding, can be a symptom of cervical cancer. Regular screening is crucial, but any unusual bleeding patterns should prompt further evaluation.
Pregnancy-Related Complications: Ectopic pregnancy or a spontaneous abortion can present with vaginal bleeding and must be considered, especially if there's a possibility of pregnancy.
Coagulopathy: Bleeding disorders, such as von Willebrand disease, can cause heavy menstrual bleeding.

Uterine Arteriovenous Malformation (AVM): A rare condition that can cause significant vaginal bleeding due to abnormal connections between arteries and veins in the uterus.
Uterine Sarcoma: A rare type of cancer that can present with abnormal uterine bleeding among other symptoms.
Adenomyosis: A condition where tissue similar to the lining inside the uterus grows into the muscular walls of the uterus, leading to heavy or painful periods, though it's not as rare as some other conditions listed here, it's less common than fibroids or DUB.