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Umbilical arteries normally originate from a pair of allantoic arteries. A failure of allantoic vascular system in early fetal life results in substitution by the vitelline vascular system, an inherent safety mechanism. This gives rise to anomalous course and origin of the umbilical artery. In these cases, the umbilical artery originates from the abdominal aorta and continues as a single umbilical artery. Aim: The aim of this study is to elaborate upon our current understanding about the origin, course and associated anomalies of Type2 single umbilical artery. Material and Methods: Fifty five foetuses, terminated for severe congenital anomalies over a period of 10 years, were sent to the department of anatomy for academic evaluation of congenital anomalies. All the foetuses were dissected systematically to delineate the abnormalities. Results: Thirty fetuses had two umbilical arteries with normal course on either side of allantois (urachus) and urinary bladder. Single umbilical artery was observed in 25 cases. Twenty had type 1 single umbilical artery and coursed normally. Five cases had single anomalous origin and course of umbilical artery, which was similar to type 2 single umbilical artery (SUA). After opening the abdominal cavity, the umbilical artery was not seen beside the urachus: instead it coursed posteriorly between the coils of intestine. When it was traced further, its origin was from the abdominal aorta. The aorta was hypoplastic below the origin of the single umbilical artery. All these cases were associated with cardiac, gastro-intestinal, vertebral, renal and limb abnormalities. Conclusion: Very few cases of this abnormality have been described in literature. Only a few of these cases were diagnosed prenatally as a vitelline artery abnormality: our study will thus help refine prenatal diagnosis and management.

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Sirenomelia also known as mermaid syndrome, characterized by fused lower limbs, is a lethal and rare congenital abnormality. This is an extreme example of caudal regression syndrome caused by vascular steal of single umbilical artery. Sirenomelia is found approximately one in 100,000 live births and is usually fatal because of complications associated with pulmonary hypoplasia, abnormal development of the kidneys and urinary bladder. Most of the cases are associated with maternal diabetes and single umbilical artery.We report a case of sirenomelia terminated at 21weeks of gestation due to multiple congenital abnormalities. Antenatal scan of a25-year old primi revealed a single live fetus of 21 weeks gestation with severe olighydramnios, non-visualization of kidneys and bladder and lower part of the spine. This pregnancy was terminated and the specimen sent to the department of anatomy for fetal autopsy. On external examination,a tail like rudimentary single midline lower limb without foot was noted. There were no external genitalia and anal orifice. Internal examination revealed hypoplastic lungs, atrial septal and ventricular septal defects, aberrant right subclavian artery, hypoplastic abdominal aorta distal to the single umbilical artery, complete agenesis of urinary system, rectal agenesis and rudimentary indeterminate gonads.We would like to discuss the clinical features, etio-pathogenesis and review of literature of sirenomelia. Early diagnosis and termination of this lethal congenital anomaly results in minimizing the trauma related to the termination of pregnancy at advanced gestation.