A normal cord has two arteries and one vein. The arteries leave the fetus for the placenta; the vein brings oxygenated blood back.
The anchor: The trap is superior vesical. The umbilical arteries arise from the internal iliac arteries; the proximal remnants later contribute to superior vesical branches.
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THE VISUAL ANCHOR
Two Out, One Back
Cord vessels break the adult oxygenation habit. Arteries are oxygen-poor because they are named by direction from the fetal heart.
Cord Cross-Section: Live
Wharton JellyGelatinous matrix cushions all three vessels.
AllantoisContributes to umbilical vessels and becomes the urachus.
Right Vein RegressesEarly embryo has two veins. Right regresses, leaving one by term.
Medial Umbilical LigamentsDistal umbilical arteries after birth. Internal iliac proximal parts stay open.
Ligamentum TeresObliterated umbilical vein. Runs in the falciform ligament to liver.
Ligamentum VenosumDuctus venosus remnant. Left hepatic vein to IVC.
INTERACTIVE
Sort Direction And Oxygen
The fastest way to stop missing this is to separate vessel name, origin, direction, oxygen content, and remnant.
Pick a chip, then place it in the correct bucket.
Artery / Out
Vein / Back
BATTLE MAP
Cord Vessel Lineup
The exam mixes count, origin, oxygenation, embryology, and adult remnants. Keep the lanes separate.
Memory Hooks
AVA: artery, vein, artery. Two out. One back.
Internal iliac is the origin. Superior vesical is the remnant trap.
Umbilical vein has the best oxygen in fetal circulation.
ELIMINATION GAME
Kill The Superior Vesical Trap
One answer has the right count but wrong origin. That is the whole trick.
Three-Vessel Cord Round
Healthy delivery. Cut cord. Three lumens visible in Wharton jelly.
Eliminate the distractors until the board move is the only one standing.
2 arteries + 1 vein
Internal iliac origin
1 artery + 2 veins
Early embryology trap
Superior vesical origin
Postnatal remnant trap
Umbilical lymphatic
No distinct lymph vessel
Oxygenated arteries
Adult habit trap
THE FLOW MAP
Placenta → Fetus → Placenta
The cord is just the highway. The board tests what happens inside the fetus: three bypasses, three vessels that obliterate at birth, and one pressure reversal that closes everything.
PLACENTA · Intervillous Space · O₂-rich
↓ umbilical vein (oxygenated blood)
LIVER · Porta Hepatis
Ductus Venosus → bypasses hepatic sinusoids → IVC
↓ IVC
RIGHT ATRIUM
Foramen Ovale → most blood shunts left → Left Atrium
Single artery, unprotected vessels, absent coiling: four clinical scenarios that change management.
HIGH YIELD
Single Umbilical Artery
Normal cord: 2 arteries + 1 vein. SUA means only 1 artery is present. Found in ~1% of singleton pregnancies.
Board associations: renal agenesis (most tested), VACTERL complex, trisomy 18, cardiac defects. Renal agenesis tops the list because the umbilical arteries and ureteric bud share the same lateral plate mesoderm developmental window.
Also remember: the proximal remnants of the umbilical arteries contribute to the superior vesical arteries after birth. That is why superior vesical is the classic distractor for the origin question.
SUA on cord inspection → ORDER renal ultrasound. Then offer genetic counseling for associated chromosomal anomalies.
ANATOMY TRAP
Velamentous Insertion
Normal: cord inserts into the body of the placental disc, protected by Wharton's jelly all the way to the placenta.
Velamentous insertion: cord inserts at the membranes. Fetal vessels travel unprotected through the chorioamniotic membranes for some distance before reaching the placenta. No Wharton's jelly. No cushion.
By itself, velamentous insertion is manageable. The danger arrives when those bare vessels happen to cross the internal cervical os.
Velamentous insertion + vessels crossing the internal os → Vasa Previa. That is the emergency.
EMERGENCY
Vasa Previa
Fetal vessels cross the internal os in front of the presenting part. At membrane rupture, those vessels rupture too.
Classic triad: painless vaginal bleeding + fetal bradycardia + sinusoidal fetal heart pattern at the moment membranes rupture. The blood is fetal blood. The baby is exsanguinating in minutes.
Diagnosis: transvaginal Doppler showing vessels at the os. Planned C-section at 34-35 weeks before labor starts. Do NOT rupture membranes artificially.
Painless bleed + fetal brady at membrane rupture → Apt test → emergency C-section. Never let vasa previa labor.
ANATOMY
Cord Coiling
A normal umbilical cord coils ~11 times in a left-handed helix (counterclockwise). Coiling provides tensile strength, prevents kinking, and allows free fetal movement.
Hypocoiling (straight cord, coiling index < 0.1 coils/cm): higher risk of cord compression and stillbirth.
Nuchal cord (cord around fetal neck): most common cord complication. Usually manageable at delivery unless severely tight.
True knot vs false knot: true knots are actual knots in the cord that restrict flow (rare, but they increase stillbirth risk). False knots are redundant folds of vessels or Wharton's jelly: benign.
Straight cord (hypocoiling) → stillbirth risk. True knot tight enough to restrict flow → also increases stillbirth risk.
BOARD-STYLE WALKTHROUGH
Clinical Vignettes
35 original clinical cases. Answers shuffle each round. Front-side exam tools work before reveal.
