Association of Transabdominal Ultrasound Evaluation of Pelvic Free Fluid Presence, Depth, Morphology, and Location with Pathology in Reproductive‐Aged Females Presenting to the Emergency Department

Objectives To evaluate the association between nontraumatic pelvic free fluid (PFF) characteristics (presence, depth, morphology, and location) and pathology in reproductive‐aged females presenting to the emergency department (ED). Methods We conducted a single‐center retrospective cohort study of patients aged 18–40 years with a uterus who were non‐pregnant or in their first trimester of pregnancy and underwent pelvic ultrasound from January 1, 2020 to December 31, 2024. Exclusion criteria were bilateral oophorectomy, known ascites, recent trauma or abdominal surgery, concurrent reproductive endocrinology treatment, or inadequate ultrasound images. The primary outcome was pathology based on a composite clinical reference standard. Two blinded, ultrasound‐trained emergency physicians reviewed point‐of‐care ultrasound (PoCUS) images for PFF presence, morphology (stripe, small pocket, large pocket, sliver), location, and maximal depth. Multivariable regression analyses evaluated associations between PFF characteristics and pathology. Receiver operating characteristic (ROC) analysis determined optimal depth thresholds for predicting pathology. Results Of 746 pelvic ultrasound examinations, 672 patients were included. Pathology was identified in 126 of 672 (18.8%) patients and PFF was present in 174/672 (25.9%). PFF was associated with pathology (adjusted odds ratio [aOR] 3.0; 95% CI 2.0–4.6). A 6.9‐mm threshold demonstrated modest discrimination for pathology (area under the receiver operating characteristic curve 0.69); mean PFF depth was 9.5 ± 7.8 mm. Stripe morphology, observed in 54 of 174 (31.0%) patients with PFF, was associated with increased odds of pathology compared with other morphologies (aOR 3.6; 95% CI 1.8–7.3; p < .001). Anteriorly located fluid relative to the uterus was associated with gynecologic pathology (aOR 3.4, 95% CI 1.2–9.4). Conclusion PFF characteristics on PoCUS may help refine diagnostic prioritization for pathology in reproductive‐aged females presenting to the ED.