Heather Demarest asked:
I'm a graduate student in the US, and really enjoy your podcast.† As I'm 7 months pregnant, I have a question about the umbilical cord.† How is it that it doesn't become tangled?† Any other long cord (dog leash, ipod headphones, etc.) quickly loops into knots and kinks that are difficult to undo.† If I recall correctly, you did a podcast describing entropy as the culprit in the headphone case.† Nevertheless, despite all the wiggling around that a fetus does, the cord typically stays knot-free.† Why is this?
Christoph - My name is Christoph Lees. I'm a Consultant in Obstetrics and Foetal Medicine at the Rosie in Addenbrookes at Cambridge.
Itís a really interesting question and a lot of women do ask us this specific question. The umbilical cord is about 30 to 60 cm in length at term. So at 36, 37 weeks it really is quite long. The important thing about it is, not only is it long, but itís really thick. So itís up to 2, sometimes 2 Ĺ cm thick, and not only does it contain two arteries and one vein. But it also contains a lot of jelly-like substance called Whartonís Jelly that protects the blood vessels. So it really is encased in quite a thick covering and then the blood vessels have jelly around them. So that stops them getting twisted or occluded in any way.
Now sometimes you can have a knot in the umbilical cord, so babies obviously move around. They jump up and down, they turn over from head down to bottom down sometimes. Why doesnít that cause the umbilical cord to knot? Well the answer is that sometimes it does, but itís very rare in fact, for a knot to cause a problem for a baby. So, because the umbilical cord is so thick, it tends not to knot itself easily and even if it does knot itself, there is so much protective jelly around the blood vessels that itís very rare that it causes a problem.
Diana - Umbilical knots do happen occasionally when a foetus swims through a loop in the cord, but the structure of the cord makes it difficult for this to have any adverse effects. There has to be a great deal of tension in order for the knot to compress the cord with any significance, and therefore, impede blood flow. CliffordK on the forum found us an article from Paediatric and Prenatal Pathology Associate in Louisville in the US. And they estimated that around 3% of preterm still births occur due to cord knots.
The umbilical cord can knot. Generally early in the term when the fetus is still small enough to travel through a loop in the cord.