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How many people are affected by or at risk for endometriosis?

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Because some women might have endometriosis, but do not have symptoms, it is difficult to know exactly how many women have the condition. Current estimates suggest that 6% to 10% of women of reproductive age have endometriosis,1,2 or approximately 5 million women in the United States.N

In 2011, the NICHD-led Endometriosis: Natural History, Diagnosis, and Outcomes study found that 11% of a group of women with no symptoms of endometriosis actually had the disorder. If this finding applies to all the women in the United States, the number of American women with endometriosis may well exceed previous estimates of 5 million.

Endometriosis is most common in women in their 30s and 40s,3 but it can affect any female who menstruates.

Factors that May Increase the Risk of Endometriosis

Studies show that women are at higher risk for endometriosis if their:

  • Mother, sister, or daughter had endometriosis (raises the risk about sixfold)3
  • Periods started at an early age (before age 11)1
  • Monthly cycles are short (less than 27 days)1
  • Menstrual cycles are heavy and last more than 7 days1

Factors that May Lower the Risk of Endometriosis

Studies also show that some factors may lower the risk for endometriosis, including:

  • Pregnancy
  • Starting menstruation late in adolescence4
  • Regular exercise of more than 4 hours a week1
  • Low amount of body fat

  1. American College of Obstetricians and Gynecologists. (2010). Management of endometriosis (Practice Bulletin No. 114). Obstetrics & Gynecology, 116(1), 223-236. [top]
  2. Giudice, L. C. (2010). Endometriosis. New England Journal of Medicine, 362, 2389-2398. [top]
  3. American College of Obstetricians and Gynecologists. (2011). Endometriosis. Retrieved December 26, 2011, from External Web Site Policy [top]
  4. Treloar, S. A., Bell, T. A., Nagle, C. M., Purdie, D. M., & Green, A. C. (2010). Early menstrual characteristics associated with subsequent diagnosis of endometriosis. American Journal of Obstetrics & Gynecology, 202, 534.e1-534.e6. [top]

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