According to WebMD, any vaginal bleeding that occurs outside of a menstrual cycle can be caused by birth control pill side effects and polycystic ovary syndrome. Birth control pills are known to cause mid-cycle bleeding within the first few months of use. Polycystic ovary syndrome is a condition that causes hormonal fluctuations that directly affect ovulation, which in turn can cause abnormal vaginal bleeding.
The Mayo Clinic explains that additional causes for vaginal bleeding outside of the normal menstrual cycle can include ovarian cysts, sexually transmitted infections or uterine fibroids, so it is important for women experiencing unusual vaginal bleeding to consult with a gynecologist to ensure proper diagnosis and treatment. Uterine fibroids are non-cancerous tumors that develop in the uterus that can lead to heavy blood loss and anemia if left untreated.
According to Women First Obstetrics and Gynecology, mid-cycle bleeding or abnormal uterine bleeding is a common sign of perimenopause, a condition that occurs in many women prior to the onset of full-on menopause. Additional symptoms of perimenopause can include heavy menstrual flow and missed menstrual periods. Women First also explains that vaginal bleeding can be indicative of uterine cancer, which can be diagnosed through tests that include pelvic exams and uterine biopsies.