Overview
This lecture covers the normal and abnormal ultrasound appearances of the umbilical cord, including its anatomy, common variants, and associated pathologies.
Normal Umbilical Cord Anatomy
- The umbilical cord connects the placenta to the fetus, supplying blood.
- It contains three vessels: two smaller-diameter umbilical arteries and one larger-diameter umbilical vein.
- Wharton's jelly surrounds and protects the cord vessels.
- The umbilical cord enters the fetus at the umbilicus (abdomen).
Single Umbilical Artery (SUA)
- Occasionally, only one umbilical artery is present instead of two.
- Ultrasound cross-section shows a single artery with the vein.
- Color Doppler is used to confirm SUA by showing blood flow only on one side of the fetal bladder.
Umbilical Cord Insertion Variants
- Normal cord insertion is at the center of the placenta.
- Eccentric insertion: cord enters near, but not at, the placental edge.
- Marginal insertion: cord enters at the placental edge.
- Velamentous insertion: cord attaches to amniochorionic membranes, not directly to the placenta; vessels are unprotected by Wharton's jelly and prone to rupture.
Vasa Previa and Funic Presentation
- Vasa previa: fetal vessels cross over the internal cervical os and lack Wharton's jelly protection.
- Funic presentation: umbilical cord overlies the cervix and floats in amniotic fluid; may resolve on its own.
- Vasa previa shows fixed fetal vessels over the cervical os, unlike funic presentation.
Other Abnormalities
- Umbilical cord cysts: usually seen in the first trimester as anechoic (fluid-filled) areas with hyperechoic (bright) borders.
- Umbilical vein varix: focal dilatation (usually ~9 mm) of the intra-abdominal umbilical vein, identified by Doppler flow near the bladder.
- Persistent right umbilical vein: intrahepatic umbilical vein curves toward the stomach instead of the right side.
Key Terms & Definitions
- Umbilical vein — vessel in the cord carrying oxygenated blood to the fetus.
- Umbilical artery — vessel(s) in the cord carrying deoxygenated blood away from the fetus.
- Wharton's jelly — gelatinous substance protecting cord vessels.
- Single umbilical artery (SUA) — occurrence of only one artery in the cord.
- Velamentous insertion — cord attaches to membranes instead of the placenta, increasing risk of vessel rupture.
- Vasa previa — fetal vessels crossing the internal cervical os, risk of bleeding.
Action Items / Next Steps
- Review sonographic images of normal and abnormal umbilical cord appearances.
- Understand how to identify cord insertion types and abnormalities on ultrasound.
- Study the definitions and significance of the key terms listed above.