At the Leuven University Fertility Centre (LUFC) of the Department of Obstetrics and Gynecology of the University Hospitals Leuven, Belgium, a retrospective epidemiological prevalence study based on an electronic search of patient files was performed to determine the prevalence of histologically proven endometriosis in a subset of infertile women with a regular cycle (variation 21 - 35 days), a partner with normal sperm and no previous surgical diagnosis of endometriosis.

In this study, the electronic files of all patients who consulted the LUFC since 2003 were searched to select women with at least 1 year of infertility, a regular cycle (variation 21 - 35 days), whose partner had normal sperm according to World Health Organization (WHO) criteria (n = 304).

After exclusion of 83 (27,3%) patients with a previous laparoscopic diagnosis of endometriosis before referral to our centre, 221 (72,7%) infertile women were included in our study.

Inclusion Criteria:

• all patients who consulted the LUFC since 2003
• with at least 1 year of infertility,
• a regular cycle (variation 21 - 35 days),
• whose partner had normal sperm according to World Health Organization (WHO) criteria.

Exclusion Criteria:

• a previous laparoscopic diagnosis of endometriosis before referral to our centre

The electronic files of all patients who consulted the LUFC since 2003 were searched to select women with at least 1 year of infertility, a regular cycle (variation 21 - 35 days), whose partner had normal sperm according to World Health Organization (WHO) criteria (n = 304).

After exclusion of 83 (27,3%) patients with a previous laparoscopic diagnosis of endometriosis before referral to our centre, 221 (72,7%) infertile women were included in our study.