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Umbilical Cord Prolapse and Other Cord Emergencies

January 16, 2011
by Marybeth Lore, MD

Assistant Professor, Department of Obstetrics and Gynecology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA

The umbilical cord is a vital intra-amniotic structure that occasionally develops catastrophic complications. Although these events are rare, understanding of risk factors, presentation, and management options can assist in positive outcomes for fetus and mother. The human fetal umbilical cord is derived from embryonic mesodermal layers and yolk sac and can be readily identified as early as the third week after conception. The cord is formed by the union of the body stalk and the omphalomesenteric duct. Within the cord are three fetal vessels: normally two arteries and one vein. Initially, there is a second (right) umbilical vein, which undergoes atrophy early in fetal life, at approximately 8 weeks. The umbilical arteries derive from the ventral branches of the paired embryonic dorsal aortas. Intraluminal pressures differ between the arteries and vein, producing differing effects during compression. Umbilical vein pressure is between 20 and 35 mmHg, and arterial, approximately 55 mmHg. Arterial compression produces bradycardia, increased arterial pressure, and fetal gasping. When only the umbilical vein is occluded, there is decreased arterial pressure, decreased femoral and carotid blood flow, but no fetal gasping. The physiologic herniation of the embryonic midgut into the cord occurs between 6 and 12 weeks, allowing for the rapid growth of the liver. The cord is covered by the amnionic epithelium and, further from the fetus, transforms from a stratified columnar to a simple columnar epithelium. The umbilical vessels are sensitive to both physical and chemical stimuli, including cold, touch, oxygen perfusion, serotonin, angiotensin, and oxytocin., Wharton’s jelly is the connective tissue of the cord that surrounds and supports the vessels. It is composed of a ground substance of open-chain polysaccharides within a fine network of microfibrils and collagen, and contains mast cells and fibroblasts.

The average length of the umbilical cord is approximately 55 cm (range 32–146 cm). The cord exhibits helical twists or coils. Over 80% of cords spiral counterclockwise and coiling can be noted as early as the ninth week of gestation, numbering about 40 turns at term. The coiling of the umbilical cord is thought to enhance the cord’s ability to withstand external forces such as tension, compression, stretching, and entanglement and also enhances flexibility. The tensile strength of the cord is directly proportional to the birth weight of the baby by approximately 2.5 times. Umbilical cords without coils appear in about 5% of fetuses, and this seems to put the fetus at increased risk for adverse outcomes such as stillbirth, fetal growth retardation, oligohydramnios, meconium-stained amniotic fluid, low Apgar scores, and intrapartum fetal distress.

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