Background: The 2004 American College of Obstetrics and Gynecology clinical management guideline states that the prevalence of endometriosis is approximately 33% in women with chronic pelvic pain (CPP). This estimate came from a review showing that 28% of adult women with CPP were found to have endometriosis. The prevalence of 28% in adult women was arrived based on a compilation of 11 published studies. Yet even within the 11 studies, the reported prevalence of endometriosis varies wildly, ranging from 2 to 74%. Such an astounding variation or heterogeneity raises the question whether it is appropriate to use a single prevalence of endometriosis for all women with CPP.
Methods: We sought to identify possible sources of heterogeneities in the estimation of prevalence of endometriosis in women with CPP. We included more studies that reported prevalence estimates than the review, and examined the effect of sample size and the year of publication on the heterogeneity.
Results: The year of publication is positively associated with the prevalence estimate, which may indicate an increasing awareness of various appearances of endometriosis, or the prevalence of endometriosis may have increased among women with CPP. An alternative analysis with removal of four studies reporting highest prevalence estimates indicated that sample size is negatively associated with the prevalence estimates while the year of publication became only marginally significant.
Conclusions: There are identifiable sources of heterogeneity in prevalence estimates, with the year of publication, sample size, and difference in evaluation of CPP being three apparent sources. Having a single prevalence estimate for all women with CPP may be too simplistic at best. The true prevalence is very likely to be higher than 33%.