The most common aberration is that of a single umbilical artery (SUA), with a cited incidence of 0.63 percent in liveborn neonates, 1.92 percent with perinatal deaths, and 3 percent in twins (Heifetz, 1984a). Fetuses with major malformations frequently have a single artery. Thus, its identiication often prompts consideration for targeted sonography and possibly fetal echocardiography. The most frequent anomalies are cardiovascular and genitourinary (Hua, 2010; Murphy-Kaulbeck, 2010). In an anomalous fetus, a single artery greatly increases the aneuploidy risk, and amniocentesis is recommended (Dagklis, 2010; Lubusky, 2007).
If target sonography inds otherwise normal anatomy, an isolated single artery in an otherwise low-risk pregnancy does not significantly increase the fetal aneuploidy risk. However, as in isolated inding, it has been associated with fetal-growth restriction and perinatal death in some but not all studies (ChettyJohn, 2010; Gutvirtz, 2016; Hua, 2010; Murphy-Kaulbeck, 2010; Voskamp, 2013). hus, while clinical monitoring of growth is reasonable, the value of sonographic surveillance is unclear.
A rare anomaly is that of a fused umbilical artery with a shared lumen. It arises from failure of the two arteries to split during embryological development. The common lumen may extend through the entire cord, but, if partial, it is typically found near the placental insertion site (Yamada, 2005). In one report, these were associated with a higher incidence of marginal or velamentous cord insertion, but not congenital fetal anomalies (Fujikura, 2003).
Found in most placentas, the Hyrtl anastomosis is a connection between the two umbilical arteries and lies near the cord insertion into the placenta. This anastomosis acts as a pressureequalizing system between the arteries (Gordon, 2007). As a result, redistribution of pressure gradients and blood flow improves placental perfusion, especially during uterine contractions or during compression of one umbilical artery. Fetuses with a single umbilical artery lack this safety valve (Raio, 1999a, 2001).
Several structures are housed in the umbilical cord during fetal development, and their remnants may be seen when the mature cord is viewed transversely. Indeed, J auniaux and colleagues (1989) sectioned 1000 cords, and in one fourth of the specimens, they found remnants of vitelline duct, allantoic duct, and embryonic vessels. These were not associated with congenital malformations or perinatal complications.
Cysts occasionally are found along the course of the cord.
They are designated according to their origin. True cysts are epithelium-lined remnants of the allantoic or vitelline ducts and tend to be located closer to the fetal insertion site. In contrast, the more common pseudocysts form from local degeneration of Wharton jelly and occur anywhere along the cord. Both have a similar sonographic appearance. Single umbilical cord cysts identified in the irst trimester tend to resolve completely, however, multiple cysts may portend miscarriage or aneuploidy (Ghezzi, 2003; Hannaford, 2013). Cysts persisting beyond this time are associated wi th a risk for structural defects and chromosomal anomalies (Bonilla, 2010; Zangen, 2010).