OC20.02: The prevalence of pouch of Douglas obliteration depicted on basic transvaginal ultrasound by a negative sliding sign in a general population

Pouch of Douglas (POD) obliteration can be predicted with a high degree of certainty in patients with symptoms of endometriosis using transvaginal ultrasound (TVS). Studies on POD obliteration and the sliding sign, as part of an expert-guided deep endometriosis (DE) TVS, have always focused on populations in tertiary care centres with high disease prevalence. Our aim is to determine the prevalence of a negative sliding sign on basic TVS in a general population. We conducted a prospective observational study at a high-volume ultrasound practice. Clinical history, indication for basic TVS, and TVS findings were documented for consecutive patients. Specifically, the sliding sign was performed to determine the POD state. Descriptive statistics were applied to the entire population and subgroups of patients high- and low-risk for endometriosis. High-risk for endometriosis was defined as having a TVS referral for endometriosis-related pelvic pain or specifically “endometriosis” and/or clinical symptoms suggestive of endometriosis. Low-risk was defined by the absence of these features. 1043 patients underwent TVS. Patients who underwent a transabdominal ultrasound (5.6%) and history of hysterectomy (1.3%) were excluded; 971 were eligible. The sliding sign was performed and interpreted in 922 patients. Prevalence of a negative sliding sign in the general, high-risk, and low-risk populations was 47/922 (5.1%), 25/243 (10.3%), 22/639 (3.4%) (p < 0.001). An axial or anteverted/retroflexed uterus was associated with a negative sliding sign (p < 0.001). We have shown that the prevalence of POD obliteration on ultrasound evaluation in the general population is roughly 1 in 20, which may serve as the foundation for future studies on the sliding sign in lower-risk populations as this dynamic ultrasound technique becomes increasingly understood and adopted.