[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Female genital tract](https://durgical.com/en/general-pathology/areas/female-genital/) › Spontaneous abortion # Spontaneous abortion - Lesion Most early miscarriages happen because the embryo has the wrong number of chromosomes; a smaller share comes from the uterus, hormones, clotting or infection. Updated Nov 12, 2026 ## Key points - Chromosomal abnormalities cause about half of first-trimester losses: autosomal trisomy (trisomy 16 the most frequent), then monosomy X and triploidy. - Maternal factors: septate uterus and other Müllerian anomalies, submucosal fibroids, cervical insufficiency (second trimester), uncontrolled diabetes, thyroid disease, luteal phase insufficiency. - Antiphospholipid syndrome: recurrent loss, decidual vasculopathy, placental infarcts and thrombi. - Infections: Toxoplasma, Listeria, cytomegalovirus, syphilis and ascending bacterial infection. - The specimen: chorionic villi (proof of intrauterine pregnancy), decidua, sometimes the embryo; hydropic or abnormal villi suggest a chromosomal cause or a mole. ## What it is Spontaneous abortion is loss of a pregnancy before the fetus can survive, and it ends a substantial share of recognised pregnancies, most in the first trimester. About half of first-trimester losses are caused by chromosome abnormalities of the embryo, mainly trisomies, monosomy X and triploidy. Maternal causes include uterine malformations, submucosal leiomyomas, poorly controlled endocrine disease, antiphospholipid syndrome and other thrombophilias, infections and toxins. Examining the products of conception confirms an intrauterine pregnancy and can reveal a molar pregnancy or clues to the cause. ## Structure - Normal-looking villi with decidua and fibrin are common in losses from any cause. - Hydropic villi with irregular outlines and trophoblast inclusions suggest an abnormal karyotype or a partial mole; circumferential trophoblast proliferation suggests a complete mole. - Decidual arteries with fibrinoid necrosis and thrombosis point to a maternal vascular cause such as antiphospholipid syndrome. - Neutrophils in the membranes or villi indicate infection (septic abortion). ## Step by step - An error in meiosis, usually maternal and more frequent with older maternal age, gives the embryo an abnormal chromosome number. - The embryo develops abnormally and the placenta forms poorly. - Alternatively, the uterus, hormones or maternal blood vessels cannot support an otherwise normal embryo. - The embryo dies, the decidua separates and bleeding and cramps expel the products of conception. ## Clinical notes - Presents with bleeding and cramping in early pregnancy; ultrasound and hCG distinguish threatened, incomplete, complete and missed abortion. - Recurrent pregnancy loss warrants a search for parental chromosome rearrangements, uterine anomalies and antiphospholipid antibodies. - Retained tissue can become infected (septic abortion) or bleed, and repeated curettage can cause intrauterine adhesions. ## Memory aid Half of early losses are a counting error: too many, too few or a whole extra set of chromosomes. ## Test yourself Think of the answer, then tap the question to see it. ## What is the most common cause of first-trimester spontaneous abortion? Chromosomal abnormality of the embryo, mainly autosomal trisomies, followed by monosomy X and triploidy. ## What does finding chorionic villi in a uterine specimen prove? That the pregnancy was intrauterine, which effectively excludes an ectopic pregnancy except in the rare combined case. ## Which acquired autoimmune disorder causes recurrent pregnancy loss with placental thrombosis? Antiphospholipid syndrome. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/spontaneous-abortion/) [More Pathology questions →](https://durgical.com/en/practice/?f=pathology) ## Elsewhere in DurgiPedia - [Placenta: structure, circulation and functions](https://durgical.com/en/embryology/placenta-structure-circulation-and-functions/) - [Uterine anomalies: bicornuate, septate, didelphys, Müllerian agenesis](https://durgical.com/en/embryology/uterine-anomalies-bicornuate-septate-didelphys-mullerian-agenesis/) - [Placenta](https://durgical.com/en/histology/placenta/) ## Connections ## Related 7 - [Hydatidiform mole: complete vs partial](https://durgical.com/en/general-pathology/hydatidiform-mole-complete-vs-partial/) - [Ectopic pregnancy](https://durgical.com/en/general-pathology/ectopic-pregnancy/) - [Acute and chronic endometritis](https://durgical.com/en/general-pathology/acute-and-chronic-endometritis/) - [Placental infections](https://durgical.com/en/general-pathology/placental-infections/) - [Chromosome abnormalities: number and structure](https://durgical.com/en/general-pathology/chromosome-abnormalities-number-and-structure/) - [Trisomies 21, 18 and 13, and the 22q11.2 deletion](https://durgical.com/en/general-pathology/trisomies-21-18-and-13-and-the-22q11-2-deletion/) - [Hypercoagulable states: inherited and acquired](https://durgical.com/en/general-pathology/hypercoagulable-states-inherited-and-acquired/) ## Related conditions 8 - [Miscarriage (early pregnancy loss)](https://durgical.com/en/conditions/miscarriage/) - [Antiphospholipid syndrome](https://durgical.com/en/conditions/antiphospholipid-syndrome/) - [Müllerian anomalies (MRKH, septate uterus, imperforate hymen)](https://durgical.com/en/conditions/mullerian-anomalies/) - [Septic and unsafe abortion](https://durgical.com/en/conditions/septic-and-unsafe-abortion/) - [Stillbirth (intrauterine fetal death)](https://durgical.com/en/conditions/stillbirth/) - [Cervical insufficiency](https://durgical.com/en/conditions/cervical-insufficiency/) - [Uterine fibroids (leiomyomas)](https://durgical.com/en/conditions/uterine-fibroids/) - [Asherman syndrome (intrauterine adhesions)](https://durgical.com/en/conditions/asherman-syndrome/) ## Microorganisms 3 - [Toxoplasma gondii](https://durgical.com/en/microbiology/toxoplasma-gondii/) - [Listeria monocytogenes](https://durgical.com/en/microbiology/listeria-monocytogenes/) - [Cytomegalovirus](https://durgical.com/en/microbiology/cytomegalovirus/) [← All of general pathology](https://durgical.com/en/general-pathology/) Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Early Pregnancy Loss (Spontaneous Abortion)](https://www.ncbi.nlm.nih.gov/books/NBK560521/) (StatPearls (NCBI Bookshelf), 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/spontaneous-abortion/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/spontaneous-abortion/