False Umbilical Cord Knot

Figure 3.7. This mid-trimester fetal demise shows an excessively long and twisted cord. Markedly twisted cords may be associated with fetal compromise or death. Such twisting is not a postmortem artifact and is seen throughout gestation. No other cause of fetal death was found on complete autopsy with karyotype.

associated with fetal morbidity and mortality (Figure 3.7). In general, one should be cautious in attributing fetal death to this or other cord problems particularly if congestion and/or thrombosis are absent. It may one of several factors, or truly incidental.

Length

One of the most obvious features of the umbilical cord is the length. This increases throughout gestation, although the growth rate slows in the third trimester. Fetal activity and stretch on the cord are major factors determining length. There is a genetic component. Normal tables have been developed (Appendices B-4 and B-5), based on the entire length. Both abnormally long and short cords have significant clinical correlates. Long cords (>75 cm) are well associated with knots and fetal entanglements. They may correlate with later hyperactivity. Congestion and thrombosis in cord vessels are important signs of true obstruction (Figure 3.8 to Figure 3.14).

Fetal Demise WeeksFalse And True Knot

Figure 3.8. The vein redundancy in false knots can be quite impressive. These are of no clinical significance and are not prone to thrombosis or hemorrhage.

False Umbilical Cord Knot

Figure 3.9. These complicated knots occurred in a 31-week infant.There is slight congestion, but no thrombosis was noted. There were no clinical signs of cord compromise. True knots and entanglements are common. Most are not associated with problems. They do occasionally cause fetal distress and death. Knots should be carefully examined for changes which suggest functionally significant obstruction.

Fetal Distress
Figure 3.10. In fatal cord compressions, flow in the vein has usually been compromised, leading to congestion on the placental side. Such was the case in this intrauterine demise.
Problems With Vessel Cord
Figure 3.11. This midtrimester loss was thought to be due to true cord entanglement and occlusion. A complete autopsy including cytogenetics failed to reveal other significant pathology.
Problems With Vessel Cord
Figure 3.12. The only source of nutrients to the umbilical arteries is the blood flow. If an artery is totally thrombosed the muscle will become necrotic allowing leakage of blood pigments which discolor the cord stroma along its course.
Coronary Artery Thrombosis Post Mortem
Figure 3.13. This three-vessel cord shows thrombosis of one artery. An occlusive thrombus in one of two umbilical arteries can occur without fetal problems because there are usually vascular anastomoses between the two arteries. This enables perfusion of the entire placenta.

Figure 3.14. This cord cross-section shows a very small artery with pigment in the surrounding tissue. Thrombosis and eventual disappearance of that vessel is a common etiology of single umbilical artery.

Figure 3.14. This cord cross-section shows a very small artery with pigment in the surrounding tissue. Thrombosis and eventual disappearance of that vessel is a common etiology of single umbilical artery.

Placental Perfusion Picture

A minimum cord length of 32 cm is felt to be necessary for normal vaginal delivery. Undue traction on the cord can cause fetal distress, cord tearing with hemorrhage, and possibly placental separation. The majority of hemorrhages in the cord will be associated with clamp marks and are artifact (Figure 3.15 to Figure 3.17). Entanglement can lead to a functionally short cord. Short cords are known to occur in disorders with

Figure 3.15. The area of hemorrhage shows a clamp mark (arrow). It is unlikely this is a true rupture of the cord and is probably not the cause of fetal distress. The majority of cord hemorrhages are an artifact, associated with cord clamping. Ideally, microscopic sections are not taken from such areas. These marks are often quite numerous from cord traction with a clamp during placental delivery.

Kocher Clamp Rupture Membranes
Kocher Clamp Rupture Membranes
Figure 3.16. This hemorrhage occurred in a stillborn infant with a short cord, complete length of 32 cm. The occlusive hematoma appeared to be arterial in origin and compressed the umbilical vein. Early thrombosis was present.

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