Definition and diagnostic criteria of retained products of conception following first-trimester pregnancy loss: a systematic review

Retained products of conception (RPOC) is a common complication following first-trimester pregnancy loss. However, there are no formal recommendations regarding the diagnosis of RPOC. This systematic review aimed to synthesise and critically appraise the existing evidence on the definition and diagnostic criteria for RPOC. We registered this systematic review prospectively with PROSPERO (CRD42023444456). A comprehensive literature search was conducted in October 2024 using the following databases: Embase (OVID), Medline (OVID), Global Health, CINAHL on EBSCOhost, Cochrane Central and Web of Science. Databases were searched using free-text keywords and subject headings for the key concepts of 'early', 'miscarriage' and 'retained'. Data were extracted and 2 by 2 tables populated. Risk of bias and quality assessments were performed using the QUADAS-2 tool. The literature search yielded 2,014 articles that were screened for eligibility, resulting in the inclusion of 17 studies in the final analysis. Ultrasound scan was the primary diagnostic tool, used in 16 of the 17 included studies. Ultrasound diagnostic markers included: endometrial thickness (ET), the presence of hyperechoic or echogenic material, and colour flow Doppler. One study used persistent bleeding for more than 14 days as the primary diagnostic marker. There was significant variation in the diagnostic thresholds used and no single ultrasound marker demonstrated consistent reliability in diagnosing RPOC. The findings of this review highlight the limitations of ultrasound as a standalone diagnostic tool for RPOC. Given the lack of clear diagnostic criteria, clinicians should integrate ultrasound findings with clinical symptoms to improve diagnostic accuracy. RPOC appears to be a distinct pathology within the spectrum of early pregnancy loss, characterised by the persistence of pregnancy tissue within the uterine cavity despite initial management which distinguishes it from incomplete miscarriage. This review provides a foundation for future research and calls for a Delphi consensus to refine the diagnosis and management of RPOC.