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A retrospective single-center analysis includes 425 FET clinical pregnancies from 2017–2021, separating HRC (n=204) and NC (n=221). RPOC is diagnosed using ultrasound, Doppler, and histopathology when available; perinatal outcomes and management are descriptively assessed. HRC shows higher RPOC rates (5.4% vs 1.4%), with elevated odds in both exact testing and Firth regression.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":40,"@type":76,"position":81},"https://docshare.wps.com/document/research-report/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/incidence-of-retained-products-of-conception-following-hormone-replacement-versus-natural-cycles-in-frozen-embryo-transfer/450390/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/incidence-of-retained-products-of-conception-following-hormone-replacement-versus-natural-cycles-in-frozen-embryo-transfer/450390.png","ImageObject",300,407,{"name":92,"@type":93},"Jake","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-05","2026-09-30",true,{"@type":102,"interactionType":103,"userInteractionCount":81},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"What question does the study address about RPOC?","Question",{"text":112,"@type":113},"Whether the incidence of retained products of conception differs between hormone replacement cycles and natural ovulation cycles in frozen–thawed embryo transfer pregnancies.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"How were pregnancies evaluated and how was RPOC diagnosed?",{"text":117,"@type":113},"The study retrospectively classified pregnancies after FET into HRC or NC. RPOC incidence was determined using ultrasound, Doppler, and histopathology when available.",{"name":119,"@type":110,"acceptedAnswer":120},"What were the main findings regarding RPOC incidence between cycle types?",{"text":121,"@type":113},"RPOC occurred in 14 of 425 pregnancies (3.3%), with a higher rate in HRC (5.4%) than in NC (1.4%), and increased odds reported by both Cochran–Mantel–Haenszel and adjusted Firth analyses.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},450390,1790785409,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":39,"category_name":40,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":81,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":52,"language":139,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":140,"faqs":141,"seo_title":142,"seo_description":67,"update_tm":143,"read_time":144},962084928904,"https://ap-avatar.wpscdn.com/davatar_155a257f0dc6eb9ab79c44ca47cae57d","Reproductive Medicine and Biology  \n ORIGINAL ARTICLE  OPEN ACCESS   \nIncidence of Retained Products of Conception Following Hormone Replacement Versus Natural Cycles in Frozen Embryo Transfer  \nAkiko Shimada1 | Yoshikazu Kitahara2 | Mitsuo Obara1 | Akiko Suto1 | Nami Tateishi1 | Misato Motegi1 | Jun Okaniwa1 | Akira Iwase2 | Kiyoshi Kamioka1  \n1HILLS Ladies Clinic, Maebashi, Japan | 2Department of Obstetrics and Gynecology, Gunma University Graduate School of Medicine, Maebashi, Japan Correspondence: Yoshikazu Kitahara ([kitahara@gunma-u.ac.jp](kitahara@gunma-u.ac.jp))  \nReceived: 24 June 2025 | Revised: 15 October 2025 | Accepted: 22 December 2025  \nKeywords: assisted reproductive technology | frozen–thawed embryo transfer | hormone replacement cycles | natural ovulation cycles | retained products of conception  \nABSTRACT  \nPurpose: This study examined whether the incidence of retained products of conception (RPOC) differs between hormone replacement cycles (HRC) and natural ovulation cycles (NC) in frozen–thawed embryo transfer (FET) pregnancies.  \nMethods: We retrospectively analyzed 425 clinical pregnancies following FET at a single center from 2017 to 2021. Pregnancies were classified as HRC (n = 204) or NC (n = 221). The primary outcome was RPOC incidence, diagnosed by ultrasound, Doppler, and histopathology when available. Management approaches and perinatal outcomes were descriptively assessed. Exact tests and Firth's penalized logistic regression were applied given the small number of events.  \nResults: RPOC occurred in 14/425 pregnancies (3.3%), with 11/204 (5.4%) in HRC and 3/221 (1.4%) in NC. The Cochran–Mantel– Haenszel odds ratio was 4.47 (95% confidence interval [CI] 1.29–16.39), and the adjusted Firth odds ratio was 3.92 (95% CI 1.18–12.96). Among RPOC cases, 5 were managed conservatively, 8 required uterine evacuation, and 1 required uterine artery embolization; histopathological confirmation was obtained in 7 cases. No significant associations were observed with embryotransfer–related procedures.  \nConclusion: HRC was associated with a higher RPOC incidence than NC. These exploratory findings suggest potential protocolrelated differences in placental separation and warrant validation in larger, prospective multicenter studies.  \n1 | Introduction  \nRetained products of conception (RPOC) refer to placental or fetal tissue that remains within the uterine cavity following pregnancy termination, miscarriage, or delivery [1, 2] . RPOC diagnosis typically involves a combination of clinical assessment and imaging. Transvaginal ultrasonography, particularly color Doppler, is widely used and demonstrates a moderate to strong correlation with the presence of RPOC [2] . However, its diagnostic accuracy is limited, particularly in cases with minimal  \nvascularity or equivocal findings. In such situations, hysteroscopy serves as a valuable adjunct, enabling direct visualization of the intrauterine pathology and facilitating simultaneous diagnosis and treatment [3] . Although dilation and curettage have traditionally been the standard treatments, hysteroscopic removal has emerged as the preferred approach because of its superior safety profile, efficacy, and reduced risk of intrauterine adhesions [4, 5] . Nevertheless, histopathological examination remains essential for definitive diagnosis and to distinguish RPOC from conditions such as endometrial polyps or gestational  \nThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.  \n© 2025 The Author(s). Reproductive Medicine and Biology published by John Wiley & Sons Australia, Ltd on behalf of Japan Society for Reproductive Medicine.  \nReproductive Medicine and Biology, 2026; 25:e70012 1 of 10  \n[https://doi.org/10.1002/rmb2.70012](https://doi.org/10.","cbCaijoeIulMzAgK","https://ap.wps.com/l/cbCaijoeIulMzAgK","pdf",290017,"English","# Abstract\n# Introduction\n## RPOC definition and diagnosis\n## Clinical implications and risk factors\n# Methods\n## Study design and population\n## Outcomes and statistical analysis\n# Results\n## RPOC incidence and management\n# Conclusion","[{\"question\":\"What question does the study address about RPOC?\",\"answer\":\"Whether the incidence of retained products of conception differs between hormone replacement cycles and natural ovulation cycles in frozen–thawed embryo transfer pregnancies.\"},{\"question\":\"How were pregnancies evaluated and how was RPOC diagnosed?\",\"answer\":\"The study retrospectively classified pregnancies after FET into HRC or NC. RPOC incidence was determined using ultrasound, Doppler, and histopathology when available.\"},{\"question\":\"What were the main findings regarding RPOC incidence between cycle types?\",\"answer\":\"RPOC occurred in 14 of 425 pregnancies (3.3%), with a higher rate in HRC (5.4%) than in NC (1.4%), and increased odds reported by both Cochran–Mantel–Haenszel and adjusted Firth analyses.\"}]","Incidence of Retained Products of Conception Following Hormone Replacement Versus Natural Cycles in Frozen Embryo Transfer | PDF",1790733060,25]