Obstetrically important lesions of the umbilical cord.

Many pathologic features of the umbilical cord affect fetal well-being adversely. Excessively long or short umbilical cords may be the cause of hematomas and thrombosis of cord vessels and the placental surface, thus causing fetal death and/or thrombocytopenia. In other cases, fetal hypoxia and central nervous system damage are possible outcomes. Thrombosis is also frequently induced by velamentous insertion of the cord, as are hemorrhages when the membranous vessels rupture during parturition. Entangling and knotting of the cord, especially of excessively long cords, may lead to similar lesions and fetal death. It was recognized recently that prolonged meconium exposure to the surface of the cord can cause partial necrosis of umbilical vessels and cord ulceration. The noxious moiety of meconium also causes contraction of the umbilical vessels, leading to fetal hypoperfusion and hypoxia. A stricture at the fetal end of the cord and excessive spiralling of a very long umbilical cord are often present in cases of unexplained fetal demise, especially in early pregnancy. Less common abnormalities are obstruction of the circulation by amnionic bands and varices.