Dr. Jeff Hersh: Can a 'nuchal cord' choke a fetus?
Q: My granddaughter was born with her umbilical cord around her neck. Luckily she is OK, but could she have choked from this?
A: The term for an umbilical cord wrapped all the way around the baby’s neck (360 degrees) is "nuchal cord." If the cord is less than all the way around it is considered just a loop of the cord lying by the fetus’ neck within the cramped conditions inside the uterus. Over 80 percent of nuchal cords go around the neck only once, but multiple wraps can occur as well.
A fetus gets her blood oxygenated via the placenta, where oxygen and nutrients are transferred to her blood from mom’s blood; the blood then passes through the umbilical cord to her body. So a nuchal cord cannot "choke" the fetus since they do not breathe in utero (while inside mom). The baby’s first breath is that cry you hear just after delivery, and that is the first time they rely on their own lungs to bring oxygen to their blood.
Some studies have shown that ultrasound identifies up to 70 percent of single wrap nuchal cords and up to 90 percent or more of multiple wrap nuchal cords that exist just prior to delivery. At the present time ultrasound is not recommended to look for a nuchal cord as a routine part of a prenatal ultrasound, but it has been used as a research tool.
Fetuses typically toss and turn quite a bit during pregnancy; ask any expectant mom about how much movement there is going on down there. It is therefore not surprising that when it is looked for there is a nuchal cord noted at some point in up to two thirds or more of pregnancies.
A nuchal cord is more common with advancing gestational age, being noted in 10 percent of fetuses of 20 weeks gestation but up to a third of full term fetuses. However, studies have shown that a "new" nuchal cord (a nuchal cord not identified on a previous ultrasound) is as likely to be seen as one previously identified, demonstrating that most nuchal cords wrap and unwrap randomly during pregnancy.
When the nuchal cord is loosely wrapped (as noted by no "hitch" preventing it from easily unwrapping) it is termed a type A nuchal cord. When there is a hitch it is called type B.
Studies have been done to look for increases in birth complications between babies born with and without a nuchal cord, and although there are many case reports of adverse outcomes, large studies have not demonstrated a statistically significant difference. Specifically, no increase in stillbirth, preterm delivery, perinatal mortality, neurodevelopmental problems or cerebral palsy has been definitively shown to be due to a nuchal cord, nor has a slowing of fetal growth (intrauterine growth retardation) or a decrease in amniotic fluid volume.
Although overall there is no definitive data showing an increased risk from nuchal cords in general, tight nuchal cords are still thought to possibly increase the risk of adverse outcomes. Therefore, clinical practice has been to try to unloop or otherwise treat nuchal cords during the birth process.
There is no definitive data to support this practice, and some experts note that doing this on a routine basis may be unnecessary and might rarely lead to other complications. However, it is thought that in those cases where a tight nuchal cord might compromise blood flow to the baby’s brain or cause other complications (such as inhibiting the birth process), treating it may be beneficial.
So, the good news is that a nuchal cord is usually not a worrisome thing (in fact one author noted that they should be considered "necklaces, not nooses"). The decision of when and if an intervention is necessary depends on the specifics of how tight the nuchal cord is and the risk it poses, and is made by the clinician in consultation with the pregnant women. Presently, no screening for a nuchal cord is recommended.
Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.