Women who are approaching menopause are at the greatest risk for fibroids because of their long exposure to high levels of estrogen. Women who are obese and of African-American heritage also seem to be at an increased risk, although the reasons for this are not clearly understood.
Research has also shown that some factors may protect a woman from developing fibroids. Some studies, of small numbers of women, have indicated that women who have had two liveborn children have one-half the risk of developing uterine fibroids compared to women who have had no children. Scientists are not sure whether having children actually protected women from fibroids or whether fibroids were a factor in infertility in women who had no children. The National Institute of Child Health and Human Development is conducting further research on this topic and other factors that may affect the diagnosis and treatment of fibroids.