Bicornuate Uterus
2026 Jan
Abstract
In 2021, the American Society of Reproductive Medicine (ASRM) Müllerian Anomalies Classification created 9 classifications: : Cervical agenesis. Müllerian agenesis. Unicornuate uterus. Bicornuate uterus. Septate uterus. Uterus didelphys. Longitucinal vaginal septum. Transverse vaginal septum. Complex anomalies . The most common subtype of Müllerian anomalies is the unification defect known as a bicornuate uterus (55.1%-73.5%). A bicornuate uterus arises from incomplete fusion of the paired Müllerian ducts during embryogenesis, typically between the sixth and tenth weeks of gestation. This anomaly results in a uterus with 2 distinct endometrial cavities and a single cervix, although variations exist (see Image. Uterus Embryology).  Clinically, a bicornuate uterus is associated with an increased risk of infertility, recurrent pregnancy loss, preterm labor, malpresentation, and adverse obstetric outcomes. Accurate diagnosis, often requiring advanced imaging modalities such as 3D transvaginal ultrasound or magnetic resonance imaging (MRI), is essential to differentiate it from other uterine anomalies like a septate uterus, which has markedly different management implications. The risk of severe maternal morbidity for a bicornuate uterus is 3.0%. In 2021, The American Society of Reproductive Medicine (ASRM) updated its Müllerian Anomaly Classification System (MAC2021) to update and expand prior classification systems in a manner that applies to all levels of healthcare providers and promotes patient awareness and advocacy. MAC2021 classifies Müllerian anomalies into 9 categories: Müllerian agenesis, cervical agenesis, unicornuate uterus, uterus didelphys, bicornuate uterus, septate uterus, longitudinal vaginal septum, transverse vaginal septum, and complex anomalies.  The septate uterus is the most commonly encountered Müllerian anomaly. ASRM defines a septate uterus with an indentation depth of >15 mm and an indentation angle of <90°. In contrast, The European Society of Human Reproduction and Embryology (ESHRE) defines a septate uterus using indentation-to-wall-thickness (I:WT) >50%, and the Congenital Uterine Malformation by Experts (CUME) suggest using an indentation depth of ≥1 cm.  Clinical determination of the need for surgical intervention for a septate uterus is challenging and controversial due to these varying yet accepted definitions. The uterus is a muscular, hollow organ in the female pelvis that is approximately 5 cm wide, 8 cm long, and 4 cm thick with a volume of 80 to 200 mL. A physiologically normal uterus typically lies in a position of anteversion (tilts forward at the cervix) and anteflexion (tilts forward at the isthmus). The uterus is situated posterior to the bladder, anterior to the rectum, and consists of four anatomical features: the fundus (top), body, isthmus, and cervix (neck of the uterus). The cervical opening into the uterus is the internal os, while the cervical opening into the vagina is the external os. There are three layers of the uterus. From external to internal: Perimetrium: continuous with the peritoneal cavity. Myometrium: smooth muscle which contracts in childbirth. Endometrium: consists of a thin base layer (stratum basalis) and a thicker functional layer (stratum functionalis). The stratum functionalis is a highly vascularized mucosal layer that undergoes monthly cyclical changes and is lost during menstruation. Uterus transplantation is today the only available treatment for absolute uterine factor infertility which is caused by either congenital/surgical uterine absence or that a present uterus is non-functioning. Structured animal-based research, from rodents to nonhuman primates, was the scientific basis for a successful introduction of uterus transplantation as a clinical procedure. The patient groups for uterus transplantation, the preclinical research and data from the published human cases will be covered herein. During recent years the concept of bioengineering of organs and tissues has emerged. Creation of a bioengineered uterus is in the initial research state, with experiments performed in rodents. The research that has been performed to create a bioengineered uterus will be summarized. In conclusion, uterus transplantation is now a clinical experimental procedure for treatment of uterine factor infertility. In parallel to the establishment of this combined assisted reproduction technique and transplantation procedure as a routine clinical procedure, we predict that uterus bioengineering will develop further towards introduction within the human setting, but that this process will take several years.
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