The umbilical cord forms from the connecting stalk during embryonic folding in the early weeks of pregnancy. By term, a normal cord measures roughly 50 to 60 centimeters in length and about 1.5 to 2 centimeters in diameter, giving it enough length to allow fetal movement without excessive tension. Running through the cord are three distinct blood vessels: two umbilical arteries carrying deoxygenated blood and waste products from the fetus to the placenta, and one umbilical vein carrying oxygenated, nutrient-rich blood back to the fetus. These vessels twist in a helical pattern, creating what are known as false knots or cord twists, which help protect the internal structures from acute compression.
Not all cords develop with the classic three-vessel anatomy. The most common vascular anomaly is a single umbilical artery (SUA), occurring when one artery either fails to form or undergoes atrophy during early development. Midwives must note that an SUA is frequently associated with congenital renal, cardiac, or chromosomal abnormalities, warranting a detailed neonatal assessment. Conversely, supernumerary vessels—such as the presence of two umbilical veins—are much rarer and can also signal underlying structural malformations that require careful pediatric follow-up after delivery.
Abnormalities in cord length can create significant mechanical risks during pregnancy and labor. A short umbilical cord measures less than 30 centimeters and can restrict fetal descent or cause placental abruption due to premature pulling. On the other hand, an excessive long cord measuring over 80 centimeters predisposes the fetus to complications such as true knots, cord prolapse, and nuchal cords where the cord wraps tightly around the fetal neck. Additionally, localized narrowing or strictures of the cord can compromise blood flow, leading to fetal distress and intrauterine growth restriction.
Normally, the umbilical cord inserts directly into the center of the placental disk. When this anatomical placement deviates, complications can arise. In a battledore insertion (marginal insertion), the cord attaches to the very edge of the placenta; while usually benign, it can occasionally weaken structural support. A more hazardous variation is velamentous insertion, where the umbilical vessels branch out across the membranes before reaching the placenta, leaving them completely unprotected by Wharton's jelly. If these exposed vessels cross the internal cervical os, the condition is known as vasa previa, presenting a life-threatening hemorrhage risk for the baby when membranes rupture.
Cord complications demand rapid, decisive midwifery intervention to prevent fetal hypoxia and mortality. During routine antenatal care, ultrasound scanning helps identify high-risk features like vasa previa or severe growth restriction linked to cord anomalies. During labor, persistent, unexplained fetal bradycardia or deep variable decelerations on the cardiotocograph often point toward acute cord compression. If cord prolapse occurs—where the cord slips down past the presenting part—the midwife must immediately elevate the presenting part digitally off the cord, place the mother in a knee-chest or exaggerated Sims position, and prepare for immediate emergency delivery.