I’ve gotten several hits on my blog about this subject, so thought I might as well go in depth with this a bit more.
The umbilical cord is what connects the baby to the mother. Soon after conception, the baby (embryo may be the “correct” term for this stage of development) burrows into the lush uterine lining, and part of the embryo becomes the placenta while the rest of it becomes the baby, inside the amniotic sac. The placenta grows along with the baby, and although the mother’s and baby’s blood never mix, the placenta is where the oxygen and waste exchange happens–the mother’s circulatory system gives the baby oxygen and nutrients while taking away the baby’s carbon dioxide and waste.
Generally, there are no problems with this wonderful system; but occasionally, the placenta does not grow very big, or the umbilical cord can develop a knot, or wrap around the baby. Many home-birthing midwives will testify that maternal nutrition plays a vital role in a well-developed placenta, which only makes sense–“you are what you eat.” Check out The Brewer Diet for more information on a healthful diet. The umbilical cord can develop a knot if the baby moves through a loop in the umbilical cord. This happens very early in pregnancy, when the baby has ample room in the womb for these free movements; later, the baby is much more squished in the confines of the uterus. Most of the time, a knot is not a problem, but a “true knot” can actually be so tight that it compromises blood flow through the umbilical cord to the baby. This is extremely rare, and usually cannot be known before birth.
Probably what most people worry about when it comes to umbilical cords is that they will be wrapped around the baby’s neck. This is called a “nuchal” cord (from the Latin word for “neck”). This is much more common, occurring in up to 20% of all births, but only rarely causes problems. My first son, for example, had the cord wrapped around his neck once, and the midwife couldn’t get it off before his body was fully born, but the cord was kept intact and my baby had no problems whatsoever. In fact, I did not even know it had happened until a few years later when I was looking through my copy of the birth records. What might cause problems is if the cord is wrapped around the baby’s neck and cuts off or diminishes circulation to the baby’s brain either in utero or as the baby is being born. But again, this is rare.
The typical response to a nuchal cord is to unloop it from the baby’s neck after the head is born and prior to full birth if at all possible; and if it’s too tight, to cut the cord and unwind it. (The cord will be clamped in two places, and the cut will be made between, to minimize blood loss to the baby, and mess on the floor from the placenta side of the cord.) Some birth attendants will instead “somersault” the baby out of the birth canal, keeping the baby’s head close to the mother’s body. This allows the baby to be born while still keeping the cord intact (occasionally, a nuchal cord might prevent the baby from coming out because it makes the cord too short). With the baby fully out, the cord can then be unwound from the baby’s neck or body, thus allowing the full amount of oxygen that sustained the baby inside to keep coming to the baby on the outside, while he makes his transition to breathing.
It may be possible to identify a nuchal cord with ultrasound, but there are some considerations you should have. First, most nuchal cords do not cause problems. There are fetal tests that can be done if a nuchal cord is suspected or known that can reassure you as to fetal well-being (including you doing “kick-counts” to make sure your baby is moving adequately). Second, ultrasound is not 100% reliable, and you have to judge the benefits vs. risks of this or any other procedure. And finally is a story one of my online friends shared with me (she is a doula at a birth center, as well as childbirth educator). A couple discovered via ultrasound that their baby had a nuchal cord (after the woman was at term, but prior to onset of labor). The woman was terrified of the baby strangling herself, so she decided to have a C-section right then. The birth center offered to keep her overnight and continue to monitor the baby, and let her see that the baby was just fine, but she was too scared to accept. Within a couple of hours, she had had the C-section, and the doctor said there was no nuchal cord. Babies move in utero; they twist and turn. It is easily understandable that the baby could wrap herself up in the cord, and then unwrap herself just as easily.