Sirenomelia dipus in a dizygotic twin.

A rare case of sirenomelia in a LBW, IUGR & second of a dizygotic twin having multiple congenital anomalies is being reported. Apart from the features of sirenomelia, the newborn had a single umbilical artery, radial hypoplasia, total anorectal & urogenital agenesis and undetermined sex. The single umbilical artery had a normal origin from the iliac artery. There was no Vitelline arterial steal phenomenon. Theories put forward regarding etiopathogenesis are discussed. We conclude that the anomalies in the present case are difficult to be explained with earlier proposed theories. This puts an emphasis on reconsideration of old theory of genetic injury to the embryo by unknown factors.