Short cord due to cord wrapping

4 Mar

One summer, I had a medical student for a project to study umbilical cord blood flow occlusion in vitro. We started with a simple set up to perfuse the umbilical cord from an elevated tank (Fig 1). We let the liquid flow in the umbilical vein and then wrapped it in various ways around a baby doll. Wrapping and twisting did stop flow. We switched to PVC pipes of different size (Fig 2). Fortunately the medical student was bright and persistent, and noted that the key factor was the length of the cord that was left after wrapping. However, I thought that we were just proving the obvious. The cord wrapping prevented twisting of the cord in the wrapped portion. The external twist was confined to the short, leftover segment. This result seemed to prove the obvious, if you twist a short piece of the cord, the twist per length of cord is high, compared to the twist over a long segment of cord. The student presented his research, but I did not think at the time it was worth trying to get published.

However, over time I realized that obstetricians were not aware of the possible significance of a short length of cord from placenta to the beginning of a wrap. They certainly were aware of the problem as “tight nuchal cord” at delivery, but not the potential for harm prior to delivery. I was persuaded to publish this by Michael Ross who reviewed and helped edit the manuscript for publication(1). This was many years after the study and sadly deprived the medical student of a publication when it might have been of more value to him. Still, I think that it is an important idea. Unfortunately it has not gotten much traction with obstetricians.

This study opened my thinking to the idea that in most cases of abnormal fetal heart rate tracing we do not know the precise anatomic cause. If we did, we might be able to see that some anatomical umbilical cord causes were going to be intractable and lead to asphyxia and that other might be ameliorated in some way. My experience with stillbirths also suggested that we were not discovering the cause of lethal asphyxia in many infants.

At the Star Legacy meeting in Minneapolis last summer Jason Collins, who has been trying to interest obstetricians in the umbilical cord during his career, showed MRI images of the fetus in situ that revealed detailed anatomic information about the cord (wrapping, position in relation to the pelvis, etc.). Such images in stillborn infants before delivery are a potential window to test hypotheses about cord compromise. Of course, studies of fetal death would lack Doppler of umbilical flow, but they could demonstrate a preponderance of short cord distances from placenta to the start of a cord wrapping, or occult prolapse between the presenting part and the pelvis. The study would not be easy to achieve with approaching parents in the midst of tragedy for permission for the study, recruiting a large delivery population(s) to have enough cases, and getting detailed pathological examination of the cord and placenta informed by the images.

Are there any obstetricians (beside Jason) out there that agree that this study should be done?

 

Reference:

  1. Bendon RW, Brown SP, Ross MG. In vitro umbilical cord wrapping and torsion: possible cause of umbilical blood flow occlusion. J Matern Fetal Neonatal Med. 2014;27(14):1462-4.

Figures:

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Fig 1: Our equipment

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Fig 2: PVC pipes

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