A true knot forms when the fetus passes through a loop of the umbilical cord, typically during early pregnancy or labor. While often benign, a true knot can tighten, especially during fetal movements or labor, leading to compression of the umbilical vessels. This compression can restrict blood flow to the fetus, potentially causing fetal hypoxia, growth restriction, and even fetal demise. The image shows a well-formed, tight knot, which is a significant finding.
| Feature | True Knot of Umbilical Cord | False Knot of Umbilical Cord | Velamentous Insertion | Battledore Placenta (Marginal Insertion) |
|---|---|---|---|---|
| Appearance | Actual intertwining of the cord, forming a loop. | Localized dilatations of Wharton's jelly or umbilical vessels. | Umbilical vessels run unprotected in membranes before placenta. | Cord inserts at the very edge (margin) of the placental disc. |
| Pathogenesis | Fetus passes through a cord loop. | Localized excess Wharton's jelly or tortuous vessels. | Abnormal placental development/implantation. | Abnormal placental development/implantation. |
| Clinical Significance | Can tighten, causing fetal compromise (hypoxia, demise). | Usually benign, no fetal compromise. | Risk of vasa previa, vessel rupture, fetal hemorrhage. | Increased risk of preterm birth, growth restriction, abruption. |
| Image Finding | Clearly visible intertwining knot. | Would appear as a bulge, not an actual loop. | Would show vessels diverging in membranes. | Would show cord attached at the periphery. |
Robbins Basic Pathology, 10th Ed, Ch 21; Williams Obstetrics, 25th Ed, Ch 27
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