A variety of umbilical cord abnormalities may be detected by prenatal sonography. These conditions include a short cord, lack of coiling, umbilical cord ulceration, a knot in the umbilical cord, umbilical artery hypoplasia, supernumerary vessels, and a variety of cystic and vascular malformations (Table 108-1) (Persutte and Hobbins, 1995). The most common abnormality, single umbilical artery, is discussed in Chapter 109.

An absolutely short cord (<35 cm at term) occurs in 0.78% of pregnancies (Skupski et al., 1992). A relatively short cord (<54 cm at term) occurs in 16.8% of pregnancies (Skupski et al., 1992). Noncoiled umbilical vessels occur in 4.3% (38of 394 pregnancies) (Strong et al., 1993). Umbilical cord ulceration is a rare abnormality. Four umbilical vessels have been notedin 0.4% (2 of 444 pregnancies) (Aokio et al., 1997). Umbilical artery hypoplasia occurs in 1.9% of pregnancies (6 of 310 high-risk patients) (Sepulveda et al., 1992). A knot occurs in the umbilical cord in 0.3% to 2.1% of pregnancies (Sepulveda et al., 1995). Vascular malformations are rare. Tumors of the umbilical cord are extremely rare.

Sonographic examination of the umbilical cord includes documentation of the number of vessels, Doppler velocimetry studies, and observation of coiling and looping of the cord (Figure 108-1). The umbilical cord is routinely examined in three locations: at the insertion site in the anterior abdominal wall of the fetus, at some point along the cord to determine the number of vessels, and at the segment floating within the cavity during assessment of amniotic fluid volume (Sepulveda et al., 1995). The umbilical cord diameter can be measured. Its diameter increases with gestational age (Ghezzi et al., 2002; Rembouskos et al., 2004). An increased umbilical cord diameter was originally thought to be a marker for aneuploidy (Ghezzi et al., 2002) but this finding was disproven in a later study (Rembouskos et al., 2004).

In extremely short umbilical cords, the cord appears to be stretched tautly across the uterine cavity (Skupski et al., 1992). Color Doppler has greatly enhanced the ability to visualize abnormalities in the umbilical cord (see Figure 108-1) (Jauniaux et al., 1989). Vascular abnormalities include umbilical artery aneurysm (Siddiqui et al., 1992), umbilical vein varix (Estroff and Benacerraf, 1992; Mahony et al., 1992; Rahemtullah et al., 2001), and persistent right umbilical vein (Jeanty, 1989; Hill et al., 1994; Wolman et al., 2002). The distance between spirals (helixes) in the umbilical cord can be measured. Normally, this distance is 2 to 2.5 cm. If the distance decreases to less than 2 cm between helixes, acute torsion of the cord is possible (Collins et al., 1993). Umbilical cord knots are difficult to identify prospectively; as many as 72% of cases are missed on third trimester color Doppler studies (Sepulveda et al., 1995). Umbilical cord cysts are found in 3% of pregnancies in the first trimester; most resolve spontaneously (Weissman and Drugan 2001). When found in the second or third trimester, there is a high incidence of structural or chromosome abnormalities (Smith et al., 1996).

The major consideration in the differential diagnosis is to determine if the umbilical cord abnormality is a false-positive finding and if it is associated with other sonographically detectable abnormalities. Many umbilical cord abnormalities are descriptive. Sensitivity and specificity of diagnosis is improved by the concurrent use of Doppler studies. The differential diagnosis for umbilical cord tumors includes hemangioma and teratoma. The differential diagnosis for cystic masses includes true cysts, pseudocysts, allantoic cysts, and hematomas.

The umbilical cord grows by tension generated by fetal movement; Naeye (1985) has measured umbilical cord lengths of 35,779 singletons and determined that a length of at least 32 cm is necessary to prevent traction on the cord during a vaginal delivery. The majority of umbilical cord growth occurs during the first and second trimesters. Walker and Pye (1960) demonstrated that the cord length of premature babies is similar to that of full-term babies. The mean length of a full-term newborn’s umbilical cord is 60 cm. There is no correlation between umbilical cord length and parity, maternal age, maternal weight or height, presence of preeclampsia, or fetal gender, weight, length, or presenting part (Walker and Pye, 1960).