Genesis of single umbilical artery

It is generally accepted that a single umbilical artery in the cord is the result of either aplasia or atrophy of the missing vessel although evidence seemingly supporting such mechanisms is seldom found. In the course of studying the development of the umbilical arteries in young human embryos another possible cause became apparent. This consisted of failure of the single umbilical artery, normally present in the body stalks of embryos of 3.0 to 4.0 mm. in length, to shorten as gestation advances. Such a situation leads to atrophy of the right or left umbilical artery within the embryo so that eventually only one vessel conveys blood from the aorta to the placenta.