ABSTRACT
The umbilical cord contains two arteries and a vein, which are embedded in Wharton’s jelly, composed of a mucoid ground substance and a network of fibroblasts. Whartons jelly protects the blood vessels from mechanical trauma. The umbilical cord is covered by amniotic epithelium. The umbilical arteries have a two-layer muscle coat that is contracted, giving the vessels an undulating appearance on histologic sections. The umbilical vein shows a less compact muscle coat (Figures 10 and 11). The umbilical vessels are arranged in a spiral fashion, with the cord usually twisting to the left. Absent twist has been associated with poor outcome including stillbirth485, and absent or right twist has been associated with single umbilical artery486. When the vessels are longer than the cord, the vessels fold, forming so-called false knots, which are of no clinical significance (Figure 75). Absence of the cord (limb-body wall complex or body stalk anomaly) is extremely rare and is associated with markedly malformed fetuses (see below in Chapter 12, discussion of Amniotic disruption sequence’)487.
