The Umbilicus

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Chapter 99 The Umbilicus

Umbilical Cord

The umbilical cord contains the two umbilical arteries, the umbilical vein, the rudimentary allantois, the remnant of the omphalomesenteric duct, and a gelatinous substance called Wharton jelly. The sheath of the umbilical cord is derived from the amnion. The muscular umbilical arteries contract readily, but the vein does not. The vein retains a fairly large lumen after birth. The normal cord at term is 55 cm long. Abnormally short cords are associated with antepartum abnormalities, including fetal hypotonia, oligohydramnios, and uterine constraint, and with increased risk for complications of labor and delivery for both mother and infant. Long cords (>70 cm) increase risk for true knots, wrapping around fetal parts (neck, arm), and/or prolapse. Straight untwisted cords are associated with fetal distress, anomalies, and intrauterine fetal demise.

When the cord sloughs after birth, portions of these structures remain in the base. The blood vessels are functionally closed but anatomically patent for 10-20 days. The arteries become the lateral umbilical ligaments; the vein, the ligamentum teres; and the ductus venosus, the ligamentum venosum. During this interval, the umbilical vessels are potential portals of entry for infection. The umbilical cord usually sloughs within 2 wk. Delayed separation of the cord, after more than 1 mo, has been associated with neutrophil chemotactic defects and overwhelming bacterial infection (Chapter 124).

A single umbilical artery is present in about 5-10/1,000 births; the frequency is about 35-70/1,000 in twin births. Approximately 30% of infants with a single umbilical artery have congenital abnormalities, usually more than one; many such infants are stillborn or die shortly after birth. Trisomy 18 is one of the more frequent abnormalities. Because abnormalities may not be apparent on physical examination, it is important that at every delivery, the cut cord and the maternal and fetal surfaces of the placenta be inspected. The number of arteries present should be recorded as an aid to the early suspicion and identification of abnormalities in the infants. For infants with a single umbilical artery but no other anomalies, the need for renal ultrasonography is controversial.

Patency of the omphalomesenteric (vitelline) duct may be responsible for intestinal obstruction, intestinal fistula with fecal or bilious draining, prolapse of the bowel, a polyp (cyst), or a Meckel diverticulum (Chapter 323.2). Therapy is surgical excision of the anomaly.

A persistent urachus (urachal cyst, sinus, patent urachus, or diverticulum) is due to failure of closure of the allantoic duct and is associated with bladder outlet obstruction. Patency should be suspected if a clear, light yellow, urine-like fluid is being discharged from the umbilicus. Symptoms include drainage, a mass or cyst, abdominal pain, local erythema, and infection. Urachal anomalies should be investigated by ultrasonography and a cystogram. Therapy is surgical excision of the anomaly and correction of any bladder outlet obstruction if present.