The paper by Bhatt et al in this issue of The Journal of Physiology brings current day analysis to age old observations regarding the appropriate timing of umbilical cord occlusion after birth (Bhatt et al. 2013). For many centuries delaying umbilical cord clamping, often until after delivery of the placenta, was part of accepted medical practice. Aristotle, for example, extolled the virtue of an intact umbilical cord for assisting in the resuscitation of newborns. ‘It often happens that the child appears to have been born dead when it is merely weak, and when before the umbilical cord has been ligatured, the blood has run out into the cord and its surroundings. But experienced midwives have been known to squeeze back the blood into the child's body from the cord, and immediately the child that a moment before was bloodless came back to life again.’ (Aristotle, ∼350 BC.)
By the 19th century cord clamping was commonly undertaken, but there was significant debate about how quickly this event should take place. One of the founders of modern academic obstetrics, John Whitman Williams, acknowledged the debate and argued against early clamping on the basis of scientific evidence. ‘The question as to the proper time for tying the cord has given rise to a great deal of discussion. Formerly it was the custom to ligate it immediately after the birth of the child; but Budin (1875) showed that 92 cubic centimetres more blood escaped from the maternal end of the cord after early than after late ligation, thus indicating that that amount was lost to the foetus by early, and saved for it by late ligation.’ (Dunn, 2007).
By the 20th century it became common practice to clamp early, typically within 30 s of birth. Some suggest that this practice was driven more by the time constraints on medical staff in busy practices, and hospital administrators to save costs on dirty linen, than rational science (Downey & Bewley, 2012). The less cynical, however, point to studies showing that early clamping appeared to reduce haemorrhage, polycythaemia and jaundice. Further, initial clinical trials suggested that in healthy term infants at least, a significant proportion of placental blood volume has relocated to the infant within the first few breaths of life, thus there was no need to delay cord clamping (ACOG, 2012).
Despite this, in the 21st century opinion remains divided on when to clamp, and there is considerable public interest in delayed clamping given data which suggest that early cord clamping may cause marked neonatal anaemia and low iron levels are associated with impaired brain development (Andersson et al. 2011). The American College of Obstetricians and Gynecologists recently concluded that there is insufficient evidence to confirm or refute the benefits of late clamping, consistent with the 2007 UK National Institute of Health and Clinical-Excellence (NICE) guidelines (ACOG, 2012). In contrast, recent Cochrane Database Reviews have suggested that there are no significant advantages for mothers in clamping early, but there are benefits, for preterm infants at least, in reducing intraventricular bleeds, necrotizing enterocolitis, blood transfusions and in generally promoting cardiovascular stability (Downey & Bewley, 2012; Rabe et al. 2012).
Haemodynamic dysfunction is known to play a role in facilitating death and injury in preterm infants. Thus improving cardiovascular stability is a clinical focus of neonatal intensive care units around the world. It has been unclear, however, what role the timing of cord clamping would play in this process. The study by Bhatt and colleagues take us back to the days of Aristotle and the question of how cord clamping can help newborns who require resuscitation. Using newborn preterm lambs, the authors have shown that umbilical cord clamping impairs the cardiovascular transition to newborn life. However, if ventilation is established before the cord is clamped, these effects are mitigated. The delay in cord clamping is in the order of 3–4 min.
So how does this work? The data suggest that this is not simply a question of changes in blood volume, but rather one of established lung function characterised by decreased pulmonary vascular resistance (PVR) and the act of breathing air. The authors show that if the cord is clamped before ventilation is established, the right-to-left shunt through the ductus arteriosus, which is normal in fetal life, is sustained. However, peripheral systemic resistance remains low, despite the loss of the placenta leading to a situation of increased after-load, reduced pre-load, and consequent significantly reduced right ventricular output. Under these circumstances blood pressure, cardiac output and cerebral perfusion become unstable. Conversely if the cord is clamped after ventilation is established, then decreased PVR allows the pulmonary bed to absorb the sharp increase in systemic perfusion that occurs when the cord is clamped and cardiac output is stabilised more rapidly.
This study highlights for us the fact that what appears to be a trivial issue on the face of it, the timing of cord clamping, may have marked physiological effects for the infant. To significantly paraphrase Aristotle on the question of art and reality; the art of umbilical cord clamping is not the outward appearance of what is being done, but its inward physiological significance. Ultimately if we are to spare our babies from injury more experimental information is needed, along with clinical trials which, as Bhatt and colleagues themselves conclude, are now warranted.