The umbilical cord connects the developing fetus to the placenta, facilitating the exchange of necessary substances. It contains one vein, which delivers oxygen and nutrient-rich blood, and two arteries, which return deoxygenated blood and waste products. These vessels are protected by Wharton’s jelly, a thick, gelatinous substance that cushions against minor compression. An umbilical cord accident (UCA) is a general term for any complication that impedes this blood flow, restricting oxygen and nutrients to the fetus.
Categorizing Umbilical Cord Complications
Complications can be categorized based on their physical mechanism, which includes compression, knotting, or vessel exposure. A nuchal cord is the most common finding, involving the cord wrapping around the baby’s neck or body, occurring in up to 29% of pregnancies. This wrapping can lead to compression or tension, particularly during descent.
A true knot is a physical knot tied in the cord, which is relatively rare, appearing in less than 1.3% of pregnancies. These knots form early in pregnancy when the fetus is small and highly mobile within the amniotic sac. Cord prolapse is an acute event where the cord slips into the birth canal ahead of the baby, where it is easily compressed between the presenting fetal part and the maternal pelvis.
Less common, but serious, issues involve the internal structure of the cord itself. Cord stricture or torsion (hyper-coiling) involves an abnormal narrowing or excessive twisting that impedes blood flow without external pressure. Vasa previa is a condition where unprotected fetal blood vessels run across the entrance to the birth canal, risking rupture and massive fetal blood loss upon membrane rupture.
Critical Timing: Risks During Pregnancy
Antepartum risks, or risks during pregnancy, are typically associated with complications that are already physically present, such as a true knot. True knots form early in gestation, around the 12th week, when the fetus is highly mobile. The knot only becomes dangerous if the baby’s movement pulls it tight, obstructing blood flow.
The risk of a true knot tightening is often linked to an abnormally long umbilical cord, which averages 50 to 55 centimeters at term. Excessive amniotic fluid, known as polyhydramnios, also contributes to antepartum risk by giving the fetus more room for extensive movement. The danger from these cord issues is often continuous and intermittent, as the knot may tighten and loosen with changes in the baby’s position.
Critical Timing: Acute Risks During Labor and Delivery
The most acute and severe umbilical cord accidents occur during the intrapartum period of labor and delivery. This is primarily because the mechanical forces of uterine contractions and fetal descent dramatically increase the potential for cord compression and tension. Cord prolapse is a sudden emergency that occurs most often after the amniotic sac ruptures, allowing the cord to wash down into the vagina before the baby.
When the cord prolapses, it is squeezed between the baby’s body and the maternal pelvis, causing immediate and severe restriction of blood flow. Similarly, a pre-existing nuchal cord or true knot can become acutely compromised during labor. As the baby descends, the cord is subjected to increased tension and pressure from the contracting uterus, which can tighten a knot or constrict vessels.
The cyclical nature of uterine contractions compresses the cord repeatedly, causing transient oxygen deprivation. This acute compression is often visible on monitoring as variable decelerations of the fetal heart rate, requiring prompt medical intervention. The rapid change in pressure and tension during the active pushing stage makes the final moments of delivery a period of heightened risk.
Monitoring and Management of Cord Concerns
Medical professionals rely on electronic fetal monitoring to detect signs of cord compression, particularly during labor. The characteristic sign is a pattern known as a variable deceleration, which appears as an abrupt drop in the fetal heart rate. These decelerations reflect a temporary decrease in blood flow through the umbilical cord, causing the fetal nervous system to reflexively slow the heart rate.
During the antenatal period, advanced imaging techniques like Doppler flow studies can assess blood flow resistance within the cord vessels, which may indicate chronic compression or structural issues. If fetal monitoring shows persistent or severe variable decelerations, immediate medical action is required to resolve the compression.
Management may involve simple interventions like changing the mother’s position to relieve pressure on the cord, or performing amnioinfusion, which involves adding saline solution to the uterus to cushion the cord. For acute, severe events like cord prolapse or non-reassuring heart rate patterns, an immediate emergency delivery, typically a Cesarean section, is the necessary response to prevent prolonged oxygen deprivation.