What is the rate of incidence for secondary amenorrhea?

In the U.S. the incident rate of secondary amenorrhea, caused by something other than pregnancy, is approximately four percent. Secondary amenorrhea, when your menstrual period stops for a period of six months or more, is more common than primary amenorrhea, which is if you've never had a menstrual period. You are more likely to have secondary amenorrhea if you have a body fat percentage under 17 percent.