The mucous membrane lining of uterus is known as decidua once it is implanted with a fertilized egg. A decidual cast forms under the influence of hormones while preparing uterus for implantation and it can shed by taking the shape of uterus. It has well known association with ectopic pregnancy. Also it can occur with incomplete abortion as mentioned in this case report. Other conditions are use of progesterone, standard dose of oral contraceptive pills. Our patient 25 year unbooked gravida 3 parity 2 with 12 week period of gestation presented to emergency department with incomplete abortion with excessive bleeding and anaemia. She was shifted for surgical evacuation in which she passed decidual cast, a very rare finding. The histopathology report suggest retained product of conception with chorionic villi.

BACKGROUND Membranous dysmenorrhea, characterized by the expulsion of intact endometrial tissue rather than gradual dissolution during menstruation, occasionally presents as a decidual cast-a complete triangular mold of the uterine cavity. This poorly understood condition is likely underdiagnosed. OBJECTIVES This study maps and describes the existing English literature on membranous dysmenorrhea and decidual cast expulsion, focusing on clinical presentation, etiology, and management. SEARCH STRATEGY A scoping review was conducted according to Joanna Briggs Institute methodology and PRISMA-ScR guidelines. PubMed, EMBASE, Web of Science, and CINAHL were searched using the terms "membranous dysmenorrhea," or "membranacea dysmenorrhea," or "decidual cast," limited to English-language publications. The final search was performed in February 2026. Google Scholar and manual screening of references supplemented the search. SELECTION CRITERIA English-language full text publications reporting on membranous dysmenorrhea or decidual cast expulsion were included, encompassing case reports, case series, and observational studies. DATA COLLECTION AND ANALYSIS Data extracted included publication type, geographical origin, patient demographics, clinical features, and management approaches. Thematic analysis was performed to identify key patterns. MAIN RESULTS One hundred and thirteen publications met inclusion criteria, including 86 case reports/series describing 121 individual cases, plus 42 additional cases from a single-author report. Patient ages ranged from 9 to 53 years. Most cases involved vaginal passage of tissue, with or without pain. Early reports noted spontaneous and recurrent episodes, while recent cases were often sporadic and involved hormonal treatments, particularly progestins. Additional associations were infection, ectopic pregnancy, pregnancy in uterus bicornis/didelphys, and postpartum hemorrhage. Proposed etiologies include hormonal influences (endogenous/exogenous progesterone), endometritis, or normal menstruation variants. Most cases resolved without intervention. Some required dilatation and evacuation of the uterine cavity. CONCLUSION Membranous dysmenorrhea and decidual cast expulsion are benign phenomena that might cause diagnostic confusion and unnecessary interventions. Increased clinical awareness is essential for appropriate counseling and to distinguish this condition from early pregnancy loss. Hormonal contraceptives might act as both triggers and therapeutic agents. Further research beyond case reports is needed.

Humans are one of the few mammalian viviparous species in which pregnancy is extended beyond the luteal phase, the phase during which progesterone is synthesized by the maternal ovary. Instead, it is the fetal placenta that produces progesterone throughout the latter 2 trimesters of human pregnancy. The placenta is developmentally crucial for reproductive success and is the most conspicuous anatomical novelty of placental mammals. However, before it can exert its dual functions as both an endocrine organ and an organ capable of facilitating gas and nutrient exchange, enormous changes must take place within the uterus to not only tolerate the presence of this hemiallogeneic tissue but to also accommodate and support placental development. The most dramatic of these changes is endometrial decidualization, the origin of which coincides in evolutionary history with invasive placentation. This article builds on the observation that the physiological changes that occur during the nonpregnant secretory phase of the uterine cycle in women are remarkably similar to that seen during pregnancy. The fundamental characteristics of human pregnancy (including endometrial decidualization followed several months later by intrauterine inflammation, uterine contractions, and discharge of the decidual lining from the uterine cavity) are present already in the nonpregnant menstrual cycle and are thus independent of the fetus. We hypothesize that many of the physiological defects that lead to complications during pregnancy and parturition are detectable already during spontaneous decidualization in the nonpregnant state and at the onset of menstruation, and can thus be determined before the onset of pregnancy.