The timing of umbilical cord clamping at birth: physiological considerations

Abstract

While it is now recognized that umbilical cord clamping (UCC) at birth is not necessarily an innocuous act, there is still much confusion concerning the potential benefits and harms of this common procedure. It is most commonly assumed that delaying UCC will automatically result in a time-dependent net placental-to-infant blood transfusion, irrespective of the infant’s physiological state. Whether or not this occurs, will likely depend on the infant’s physiological state and not on the amount of time that has elapsed between birth and umbilical cord clamping (UCC). However, we believe that this is an overly simplistic view of what can occur during delayed UCC and ignores the benefits associated with maintaining the infant’s venous return and cardiac output during transition. Recent experimental evidence and observations in humans have provided compelling evidence to demonstrate that time is not a major factor influencing placental-to-infant blood transfusion after birth. Indeed, there are many factors that influence blood flow in the umbilical vessels after birth, which depending on the dominating factors could potentially result in infant-to-placental blood transfusion. The most dominant factors that influence umbilical artery and venous blood flows after birth are lung aeration, spontaneous inspirations, crying and uterine contractions. It is still not entirely clear whether gravity differentially alters umbilical artery and venous flows, although the available data suggests that its influence, if present, is minimal. While there is much support for delaying UCC at birth, much of the debate has focused on a time-based approach, which we believe is misguided. While a time-based approach is much easier and convenient for the caregiver, ignoring the infant’s physiology during delayed UCC can potentially be counter-productive for the infant.

Postnatal cardiovascular adaptation

“…The LV suffers from reduced preload as FO shunting decreases with cessation of umbilical venous return, at the same time afterload increases as the compliant placental circulation is removed 69. If the placental circulation remains intact until pulmonary blood flow is established, physiologically-based cord clamping (PBCC), then haemodynamic compromise is minimised and insult to the LV reduced 70. PBCC has also been shown to confer advantages in the asphyxiated animal model 71.…”

Delayed cord clamping was not associated with an increased risk of hyperbilirubinaemia on the day of birth or jaundice in the first 4 weeks

“…The optimum timing of cord clamping is believed to have a positive effect on the placental transfusion rate and, therefore, neonatal and infant circulation . Uterine contractions, lung aeration, spontaneous inspirations, crying, the timing of cord clamping and the effect of gravity are associated with placental transfusion to the baby . This placental transfusion mainly takes place within 2 minutes, but sometimes it continues up to 5 minutes after birth.…”

Optimising Intravenous Volume Resuscitation of the Newborn in the Delivery Room: Practical Considerations and Gaps in Knowledge

“…However, the authors advise that, until further evidence is available, placental transfusion should be discontinued in infants who are not breathing, so that resuscitation measures are not delayed [1]. They acknowledge that even though there is compelling physiological data from animal studies to suggest many benefits to resuscitating depressed newborns whilst on the cord, such a recommendation has not been formulated in the ILCOR or ERC guidelines due to the lack of human studies on the feasibility and safety of this approach [59,60]. First-in-human studies are currently underway.…”