This is the second in a two-part series on umbilical cord-related issues. The first article dealt with cord blood banking.
One of the criticisms that has been leveled against the typical hospital birthing environment is the “assembly line” approach to delivering a baby. In many cases, obstetricians and obstetric nurses have a time frame in which they want to see events take place. It’s been argued that the high Cesarean section rate in the U.S. is among the consequences of this approach. While it’s easy to sit in an armchair and criticize the medical establishment for being too eager to intervene in “normal” deliveries, too quick to augment labor, give medications and episiotomies, and too fast to cut the cord and swoop off with the newborn to measure, bathe, and inoculate, it’s important to remember that there are legitimate medical reasons for many of these interventions (and the speed with which they’re carried out). No, normal birth is not an emergency. However, we live in a very, VERY litigious society, and obstetricians are at exceedingly high risk of being sued. Ever wondered why there aren’t many old obstetricians? It’s not because they burn out or get bored; many truly enjoy their work. It’s because they can be sued by (or on behalf of) each child they deliver until that child turns 18. As such, an obstetrician must continue to carry malpractice insurance for 18 years after the last delivery they attend. Given that malpractice insurance can cost an obstetrician nearly $100,000 a year (a figure impossible to afford when there’s no income to support it), most OBs stop doing deliveries and revert to simple gynecology approximately 20 years before they plan to retire for good. Gives a new perspective on why your OB is quick to intervene, doesn’t it?
In any case, clamping the umbilical cord, which contains the blood vessels that carry oxygen and nutrients from mother to child during pregnancy, is one of the procedures that takes place after delivery. In the case of an emergency — a baby who is born in need of resuscitation, for instance — the cord is clamped immediately so that medical professionals can work freely on the newborn. In the case of a normal, non-emergent delivery, however, there’s been some debate as to when the cord should be cut for the best outcome.
Remember from high school physics that, for each action, there’s an equal and opposite reaction. What this means is that when your baby puts an incredible amount of pressure on your cervix and the tissues of your vagina to stretch them during labor (ouch!), your tissues respond by putting an incredible amount of pressure on your baby in return. Bottom line, your baby gets squeezed — hard — as he or she travels through the birth canal. When a baby who is still connected up to the placenta via an umbilical cord gets squeezed, the result is that blood from the baby literally get squeezed right out the cord and into the placenta.
Imagine, for a moment, a cave-woman giving birth. Once her baby was out, she (or her female attendants) would pick him up and put him to her breast. Cave-mama would cuddle cave-baby and warm him up, and her female attendants would stand around smile and enjoy the beautiful, peaceful scene. Eventually (and this part is speculative, but it’s reasonable and measured speculation), someone would tear the cord (probably using a sharp rock). It’s possible to imagine a similar scenario in, say, pre-Industrial England (but without the cave, and with a scissors instead of a rock). Bottom line, before birthing took place in a hospital, there would have been a natural time gap between the birth of a baby and the returning of the attendants’ attention to the matter at hand (namely, the afterbirth). During this time gap, the baby’s heartbeat would have continued to circulate blood throughout the baby’s body, the umbilical cord, and the placenta. Over the course of several minutes, the quantity of blood in the baby — while low immediately after birth — would have returned to normal. Several minutes later, post-delivery changes in circulation would cause the vessels in the cord to clamp down, naturally sealing the baby off from the placenta and keeping the baby’s blood entirely within its body. At this point, the cord would stop pulsing. A baby allowed to remain attached to the cord until it stops pulsing on its own ends up with a much higher red blood cell count than one who is immediately disconnected; this improves iron status (red blood cells need iron to function), and reduces the need for dietary iron early in life. In fact, breast milk may be low in iron (see an excellent article at Science of Mom on this topic) simply because babies who don’t have their cords cut early don’t need supplemental dietary iron early in life.
Because immediate cord clamping doesn’t allow blood volume in the baby to return to normal, it increases the risk of low neonatal hemoglobin (a marker of too few red blood cells, which can impair oxygen delivery, and leads to increased risk of anemia later in the first year of life). This is associated with a number of potential negative outcomes, including delayed development. Many studies have examined the benefits associated with delaying cord clamping, as opposed to clamping the cord immediately (see, for example, Andersson et al, Ceriani Cernadas et al, Hutton et al, Ultee et al). The studies indicate that the best time to clamp the cord so as to avoid the risk of low neonatal hemoglobin is at approximately three minutes post-delivery.
On the other hand, there’s been speculation (and there’s a small amount of evidence) of risks associated with delayed cord clamping. For instance, Prendiville et al found that delayed clamping can increase the risk of polycythemia (too many red blood cells, proportionally speaking) and hyperbilirubinemia (too much bilirubin, a breakdown product of red blood cells, which leads to jaundice). However, these results haven’t been reproduced in the vast majority of delayed cord clamping studies. Andersson et al, Ceriani Cernades et al, and Ultee et al found no significant increased risk of negative outcome (jaundice or otherwise) with delayed cord clamping (at three minutes post-delivery in each study). Hutton et al found an increased risk of polycythemia in infants whose cords had been clamped at least two minutes post-delivery, but also found that the condition was not associated with any negative outcomes. There is an unpublished study (Mc Donald, PhD thesis) that suggests very delayed cord clamping (5 minutes or longer post-delivery, or when the cord stops pulsing) may increase the risk of jaundice requiring light therapy. While these results have not been replicated elsewhere, it’s probably worth being cautious with extremely delayed cord clamping.
Somewhat delayed cord clamping also appears to benefit premature and low birth-weight babies, though very premature babies are generally born under medically urgent circumstances, and delaying clamping by several minutes is not likely to be feasible. The aforementioned Ultee study focused on slightly premature infants (delivered between 34 and 36 weeks), and showed higher hemoglobin with a three-minute delay. A study of very premature infants (around 28-29 weeks gestational age) found that delaying clamping as much as 30-45 seconds post-delivery as opposed to clamping immediately helped to reduce the otherwise significant risks of late-onset sepsis (infection) and intraventricular hemorrhage (bleeding in the brain) (Mercer et al). The Mercer study didn’t examine the effects of waiting longer than 30-45 seconds, simply because of the emergent nature of extremely preterm births. The authors pointed out that, of course, many very preterm babies would require immediate care, precluding the possibility of waiting even 30 seconds to clamp the cord, but recommend on the basis of their findings that, whenever possible, clamping be delayed a bit. A similar study by Rabe et al found that premature babies in the range of 29-33 weeks gestational age generally had good outcomes when cord clamping was delayed by 45 seconds, despite the delay, and benefited from the delay in terms of reduced need for transfusion.
Science Bottom Line:* If there’s no medical emergency that requires separating baby from mother immediately, the evidence supports waiting three minutes to cut the cord. During this time, the baby should be at the level of the mother (ideally on her chest) to ensure that gravity neither prevents nor inappropriately augments the return of blood into the baby.
Are you in favor of delayed cord clamping?
Andersson et al. Effect of delayed versus early umbilical cord clamping on neonatal outcomes and iron status at 4 months: a randomised controlled trial. BMJ. 2011 Nov 15;343:d7157. doi: 10.1136/bmj.d7157.
Ceriani Cernades et al. The Effect of Timing of Cord Clamping on Neonatal Venous Hematocrit Values and Clinical Outcome at Term: A Randomized, Controlled Trial. Pediatrics. 2006 Apr;117(4):e779-86. Epub 2006 Mar 27.
Hutton et al. Late vs Early Clamping of the Umbilical Cord in Full-term Neonates. JAMA. 2007 Mar 21;297(11):1241-52.
Mercer et al. Delayed Cord Clamping in Very Preterm Infants Reduces the Incidence of Intraventricular Hemorrhage and Late-Onset Sepsis: A Randomized, Controlled Trial. Pediatrics. 2006 Apr;117(4):1235-42.
Prendiville et al. Care during the third stage of labour. In: Chalmers I, Enkin M, Keirse MJNC editor(s). Effective care in pregnancy and childbirth. Oxford: Oxford University Press; 1989:1145–69.
Rabe et al. A randomised controlled trial of delayed cord clamping in very low birth weight preterm infants. Eur J Pediatr. 2000 Oct;159(10):775-7.
Ultee et al. Delayed cord clamping in preterm infants delivered at 34 36 weeks’ gestation: a randomised controlled trial. Arch Dis Child Fetal Neonatal Ed. 2008 Jan;93(1):F20-3. Epub 2007 Feb 16.