Chapter 28: The Umbilical Cord

THE NORMAL UMBILICAL CORD

The umbilical cord links the fetus to the placenta and is the fetal lifeline. The cord is between 30 and 60 cm in length, the average being 50 cm. It is covered on the outside by amnion, which blends with the fetal skin at the umbilicus. On the inside of the cord is the thick myxomatous Wharton jelly. Through the jelly, protected by it, run the umbilical vessels, one vein and two arteries, in a spiral arrangement. The circulation is the reverse of the adult in that the vein carries the oxygenated blood to the fetus, and the arteries bring venous blood back to the placenta.

The fetal surface of the placenta is covered by amniotic membrane, under which course the large blood vessels, branches of the umbilical vein and arteries. Normally the cord inserts into the center of the placenta.

ABNORMALITIES OF THE UMBILICAL CORD

Length

Cords have been reported to measure as short as 0 cm and as long as 104 cm.

1. A short cord may result in delay in descent of the fetus, fetal distress, and separation of the placenta from the wall of the uterus, inversion of the uterus, and rupture leading to hemorrhage and possible fetal exsanguination

2. A long cord is subject to entanglement, knotting, encirclement of the fetus, and prolapse

3. When the cord is absent, the fetus is attached directly to the placenta at the umbilicus. Body stalk anomaly is seen accompanying the absent cord. Amniotic band syndrome is associated with the pathogenesis

4. It appears that the length of the umbilical cord is determined at least partly by the amount of amniotic fluid present in the first and second trimesters of pregnancy and on the mobility of the fetus. If there is oligohydramnios, amniotic bands, or limitation of fetal movement for any reason, the umbilical cord will not develop to an average length

SINGLE UMBILICAL ARTERY

This occurs in 1 percent of single births and in 7 to 14 percent of multiple pregnancies. If isolated, there is a 15 percent risk of intrauterine growth restriction (IUGR) in the pregnancy. If other anomalies are present, there is a 50 percent aneuploidy risk. There is no association with trisomy 21.

Umbilical Cord Cyst

There is a 2 percent prevalence of umbilical cord cyst. Most often these are a transient finding in the first trimester. If they are transient, they have a very good prognosis. They may be associated with trisomy 13 and 18, and they have a poorer prognosis if they are multiple.

UMBILICAL VESSEL ANEURYSM

An umbilical vein varix is present if the vein measures more than 9 mm in diameter. This is usually seen in the intraabdominal portion of ...