Strengths and limitations
The majority of previous studies that have estimated the prevalence of endometriosis were focused on women who were symptomatic of pelvic pain or were undergoing fertility tests. Our study is the first to describe the prevalence of endometriosis in women during pregnancy, regardless of their previous gynaecological history. We found that the prevalence of endometriosis in women attending our early pregnancy unit (5%) was similar to that in women attending our general gynaecological diagnostic clinic (6%).13
The main strength of our study is that it is a large prospective study with clearly defined diagnostic criteria. All examinations were performed by a single operator to avoid inter-observer variability. Consecutive women were screened using a consistent approach to ultrasound examination technique and the same high-quality ultrasound technology. Consistent data collection was ensured and included multiple demographic and clinical variables in order to examine possible associations with the presence of endometriosis.
A possible limitation of our study is the lack of surgical or histological confirmation of the diagnosis of endometriosis. However, the diagnostic criteria were clearly defined in the study methodology and expert ultrasound examination has been well-described in the literature as having good concordance with laparoscopy for the detection of moderate and severe endometriosis.11 In addition, superficial peritoneal disease cannot be reliably detected on transvaginal ultrasound and therefore the true prevalence of endometriosis is likely to be higher than found in our study. However, the clinical significance of superficial peritoneal endometriosis has been recently questioned and its relevance in the context of adverse pregnancy outcomes is unlikely to be comparable to that of ovarian and deep disease.21 We were unable to detect deep or ovarian endometriosis in some women who reported past diagnosis of endometriosis. However, the subtype of their previous diagnosis was not known and more than 80% had previously undergone surgical treatment.