According to the Center for Menstrual Disorders and Reproductive Choice, the main difference between fibroids and polyps lies in their origins. Fibroids are benign tumors of uterine muscle tissue, while polyps are benign tumors of the uterine lining (endometrial tissue).
According to uterine-fibroids.org, between 25 and 50 percent of women suffer from benign tumors found in the muscle of the uterus during their childbearing years. They can vary in size, and they grow either singularly or in a cluster.
As Mayo Clinic explains, polyps are the main cause of heavy menstrual bleeding and are believed to be the most common cause of heavy bleeding after menopause. Like fibroids, polyps are usually benign, but they can be associated with cancer in older women, according to the Center for Menstrual Disorders and Reproductive Choice.