Physiological-Based Cord Clamping
During birth a baby transitions from relying on the natural support in the womb of the mother, into breathing and living on its own strength.
A process involving major physiological changes in the newborn baby.
This animation explains what happens with the baby’s heart and blood-flow during this transition and how the timing of clamping the umbilical cord is of critical importance to the baby’s health.
Physiology
Before a baby is born, when it is still a fetus safely in the womb of its mother, it receives oxygen-rich blood from the placenta via the umbilical cord. During birth, the baby transitions from the support of the placenta to autonomous breathing and circulation, a magical process involving major circulatory and hemodynamic changes.
Newborn and adult circulation
In babies and adults, all the blood flows from the right side of the heart through the lungs, to be oxygenated, back to the left side of the heart. The left side then pumps the oxygenated blood into the body, to provide oxygen and nutrients to our cells. De-oxygenated blood then returns back into the right side of the heart.
Fetal circulation
Fetal circulation is different to the circulation of a newborn baby and an adult. In the fetus, not much blood passes through the lungs. The fetus is not breathing air and the lungs are filled with fluids. Rather, it receives oxygen-rich blood from the placenta via the umbilical cord. In fetal circulation, the placenta mainly supplies blood to the left atrium, through an anatomical opening called the foramen ovale.
Aside for the patent foramen ovale, there is another important connection, the patent ductus arteriosus, the connection between the pulmonary artery and the aorta, allowing blood to travel through the pulmonary artery to bypass the lungs and go straight into the aorta. Blood can bypass the lungs because of high vascular resistance in the pulmonary arteries, allowing the blood to more easily flow into the aorta.
In the fetus, oxygenated blood flows through the umbilical vein to the liver and passes through the ductus venosus before joining with the inferior vena cava. The blood will enter the right atrium and then either go into the right ventricle or it will go through the patent foramen ovale into the left atrium, before being pumped in the left ventricle and into the (ascending) aorta. The blood that is pumped from the right ventricle can go through the pulmonary artery to enter the lungs, but mainly bypasses the lungs straight into the (descending) aorta via the patent ductus arteriosus. Through the aorta, blood flows into the fetal body and back to the placenta via the umbilical arteries.
Transition during birth^3-6^
After birth, when the baby takes its first breaths, its lungs fill with air. With these first breaths, the lungs start to expand and the alveoli in the lungs are cleared of fluids. Pulmonary vascular resistance reduces, allowing a fast increase of pulmonary blood-flow. This leads to a steady change of blood-flow: it is no longer the mother’s placenta, but the pulmonary blood flow that provides all the blood to the left atrium, stimulating the foramen ovale to close. The umbilical cord can now be safely clamped, thereby separating the baby from its placenta. The baby’s first breaths are crucial to redirect blood-flow to start passing through its lungs, triggering a steady transition to autonomous circulation.
Early cord clamping^3-7^
Around 1 in 10 babies do not breathe (sufficiently) at birth. Around the world, this affects over 35,000 newborns every day. Todays medical convention prescribes to cut the umbilical cord soon after birth, in order to provide urgent care. The placental circulation is cut off before the baby’s lungs are filled with air.
Clamping the umbilical cord before the baby aerates it's lungs can be harmful.
The first problem of clamping the umbilical cord so soon, is that blood, that was returning from the baby back into the placenta, is now all redirected through the baby’s body. Systemic vascular resistance increases and as a result, there is a very rapid increase in arterial pressure. This increases by at least 30% in only 4 heartbeats.
Secondly, the left side of the heart is deprived of venous return or preload. The blood-flow from the placenta into the heart is cut off while at the same time the pulmonary blood-flow remains low. The baby’s heart has less blood to pump, its heart rate will drop and cardiac output greatly decreases by up to 50% in only 60 seconds, thereby reducing the supply of vital oxygen to the baby’s organs, especially the brains.
The rapid increase in blood-pressure and the reduced oxygen supply to the organs, can cause injury, especially to the baby’s brains and intestines.
A recent meta-analyses in preterm infants, performed by the iCOMP collaboration, confirmed that early cord clamping ranked worst for the outcome of death before discharge and key secondary outcomes.^7^
Only after the baby’s lungs fill with air, redirecting the blood-flow through the lungs, the left atrium will be supplied with sufficient blood, to restore cardiac output.
Placental transfusion and circulation^8^
By keeping the umbilical cord intact, placental circulation and blood-flow from and to the baby is maintained for some minutes after birth. This blood is re-distributed to the baby’s organs, gradually transfusing blood volume from the placenta to the baby, delivering oxygen and important nutrients like iron.
In term neonates, the blood-flow from the placenta contributes to an additional 80-100ml circulating blood volume. This adds around 30% circulating blood-volume, including around 20-30mg/kg iron.
Research shows ^8^ that gravity has little to no effect on placental transfusion and circulation. The main driver for placental circulation is the baby’s breathing, causing a pressure difference that “pulls” blood into its own circulation.
Physiological-based cord clamping
Physiological-based cord clamping means waiting with clamping the umbilical cord at a time until after the baby has aerated it's lungs, started breathing and has completed its physiological transition. The timing of cord clamping is guided by the baby’s own condition, instead of a fixed time.
Allowing the baby to aerate its lungs before clamping the cord, leads to a gentle switch from the oxygen-rich blood-flow from the placenta to autonomous breathing and blood flow. This prevents a rapid increase in blood-pressure and sustains heart rate and cardiac output and thus the supply of vital oxygen to the baby’s organs.
Intact cord stabilization
Around 1 in 10 babies do not breathe (sufficiently) at birth. These babies need respiratory support immediately after birth. To offer these babies the benefits of physiological-based cord clamping, respitatory support can be provided while keeping the umbilical cord intact.
The baby’s vital signs are used to determine when the cord can be clamped:
- Heart Rate > 100 bpm
- SpO2 > 85%
- FiO2 < 40%
- Preferably spontaneous breathing on nCPAP
Birth can be improved
Literature references
- Healthy Newborn Network
- WHO fact sheet
- Bhatt S, Alison BJ, Wallace EM, Crossley KJ, Gill AW, Kluckow M, et al. Delaying cord clamping until ventilation onset improves cardiovascular function at birth in preterm lambs. J Physiol 2013 Apr 15;591(Pt 8): 2113-26. https://doi:10.1113/jphysiol.2012.250084
- Hooper SB, Kitchen MJ, Polglase GR, Roehr CC, Te Pas AB. The physiology of neonatal resuscitation. Curr Opin Pediatr. 2018 Apr;30(2):187-191. https://doi:10.1097/MOP.0000000000000590.
- Hooper SB, Te Pas AB, Lang J, van Vonderen JJ, Roehr CC, Kluckow M, Gill AW, Wallace EM, Polglase GR. Cardiovascular transition at birth: a physiological sequence. Pediatr Res. 2015 May;77(5):608-14. https://doi:10.1038/pr.2015.21.
- Polglase GR, Dawson JA, Kluckow M, Gill AW, Davis PG, te Pas AB, et al. Ventilation onset prior to umbilical cord clamping (physiological-based cord clamping) improves systemic and cerebral oxygenation in preterm lambs. PLoS One 2015;10(2): e0117504. https://doi.org/10.1371/journal.pone.0117504
- Seidler AL, Libesman S, Hunter KE, Barba A, Aberoumand M, Williams JG, Shrestha N, Aagerup J, Sotiropoulos JX, Montgomery AA, Gyte GML, Duley L, Askie LM and iCOMP Collaborators. Short, medium, and long deferral of umbilical cord clamping compared with umbilical cord milking and immediate clamping at preterm birth: a systematic review and network meta-analysis with individual participant data. The Lancet Published Online November 14, 2023, https://doi.org/10.1016/S0140-6736(23)02469-8.
- Yao AC, Moinian M, Lind J. Distribution of blood between infant and placenta after Birth. The Lancet 1969 Oct 25. https://doi.org/10.1016/S0140-6736(69)92328-9
- Ronny Knol, Brouwer E, Vernooij ASN, et al. Clinical aspects of incorporating cord clamping into stabilisation of preterm infants Arch Dis Child Fetal Neonatal https://doi:10.1136/archdischild-2018-314947.
- Brouwer E, Knol R, Vernooij ASN, et al. Physiological-based cord clamping in preterm infants using a new purpose-built resuscitation table: a feasibility study Arch Dis Child Fetal Neonatal 2018. https://doi:10.1136/archdischild-2018-315483.
- Ronny Knol, Emma Brouwer et al. PBCC in very preterm infants, RCT on effectiveness of stabilisation. Resuscitation 147 (2020) 24-33. doi: https://10.1016/j.resuscitation.2019.12.007.
- Ronny Knol, Emma Brouwer et al. Physiological versus time-based cord clamping in very preterm infants (ABC3): a parallel-group, multicentre, randomised, controlled superiority trial. The Lancet Regional Health Europe Published December 4, 2024. https://doi:10.1016/j.lanepe.2024.101146.
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