Overall about 40 % (20% to 80%) of women will develop fibroids by age 50. The average age range when symptoms start is 35-50. African American women appear to be more prone to developing fibroid tumors. Asian women have the lowest incidence. Obesity has been described as a risk factor. The levels of reproductive estrogen and progesterone hormones in the body do play an important role. In fact, fibroids may grow rapidly during pregnancy and the growth will slow after menopause.