Dysfunctional Uterine Bleeding (DUB): This is the most common cause of abnormal uterine bleeding in women of reproductive age, often related to hormonal imbalances, particularly anovulatory cycles. It's a diagnosis of exclusion after ruling out other causes.

Uterine Fibroids: Common in women of reproductive age, fibroids can cause prolonged and heavy menstrual bleeding due to their location, size, and number.
Endometrial Hyperplasia: This condition, often associated with unopposed estrogen, can lead to prolonged and heavy menstrual bleeding.
Polycystic Ovary Syndrome (PCOS): Although PCOS is more commonly associated with oligomenorrhea or amenorrhea, some women may experience prolonged menses due to hormonal imbalances and anovulatory cycles.
Thyroid Disorders: Both hypothyroidism and hyperthyroidism can affect menstrual regularity and duration, leading to prolonged menses in some cases.

Pregnancy Complications: Although less likely in a 27-year-old without a reported pregnancy, ectopic pregnancy or a molar pregnancy can present with abnormal vaginal bleeding and must be ruled out due to their potential severity.
Cancer (Endometrial, Cervical, or Uterine): Although rare in young women, any abnormal uterine bleeding warrants investigation to rule out malignancy, especially if risk factors are present.
Bleeding Disorders (e.g., von Willebrand Disease): These conditions can lead to heavy and prolonged menstrual bleeding and are critical to diagnose due to their implications for future health and potential treatments.

Adenomyosis: A condition where endometrial tissue grows into the uterine wall, leading to heavy and prolonged menstrual bleeding, though it's more commonly diagnosed in older women.
Uterine Arteriovenous Malformations: Rare vascular anomalies that can cause abnormal uterine bleeding.
Systemic Diseases (e.g., Chronic Kidney Disease, Liver Disease): Certain systemic conditions can affect coagulation and lead to abnormal bleeding patterns, including prolonged menses.