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.

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.

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.

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

Time Based Cord Clamping^7-11^

A lot of clinical research has been done in recent years to research the benefits of delaying cord clamping. Most studies compare immediate cord clamping with the benefits of Time Based Cord Clamping, clamping the cord after a fixed time of 60-120 sec. Time Based Cord Clamping is also referred to as Delayed Cord Clamping.
Meta-analyses shows a number of benefits of Time Based Cord Clamping:

• Less anemia;
• Reduced need for blood transfusions;
• Reduction in mortality by 33%;
• Possible reduction in the risk of bleeding in the brain (IVH) and necrotizing enterocolitis (NEC).
  

There is no evidence of any adverse impact or harm for the baby or the mother.

Physiological-based cord clamping means clamping the umbilical cord at a time when the baby is fully stable and breathing on its own. The timing of cord clamping is determined 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.

A study in preterm lambs comparing cord clamping before and after the onset of ventilation, shows the rise in pulmonary blood-flow and the stable arterial pressure and heart rate in the ventilated group compared to the unventilated group.^3^

Avoiding bradycardia and hypoxemia in the first minutes after birth, is associated with a reduced risk of brain hemorrhage (IVH) or death.^13^

Proven feasibility^12^

The positive effects of physiological-based cord clamping for preterm babies has for the first time been shown in a recently published feasibility study. In total 33 babies born <35 weeks’ gestational age received physiological-based cord clamping with the Concord Birth Trolley at Leiden University Medical Center.

In this study, heart rate remained stable around the moment of cord clamping and no bradycardia was observed after clamping the cord. Oxygen levels in the blood (SpO2) increased at a faster pace when comparing with preterm infants receiving immediate cord clamping and the duration of hypoxemia was shorter in the first 10 minutes after birth.

Recently, a large multicenter randomized trial started, to investigate the effects of physiological-based cord clamping: the ABC3 trial, led by Prof. Arjan te Pas, from Leiden University Medical Center.

ABC is the abbreviation for “Aeration, Breathing then Clamping”, referring to a “new” ABC protocol for neonatal resuscitation, based on physiological-based cord clamping.

The objective of the trial is to investigate the effect of physiological-based cord clamping compared to time based cord clamping (of 60 sec) without stabilization. Around 700 preterm born infants <30 weeks gestational age will be recruited in this study, that is performed by a consortium of Dutch and international hospitals.

The primary outcome of ABC3 is an absolute increase in intact survival at hospital discharge, defined as survival without cerebral injury (IVH >grade 1 and/or PVL >grade 1 and/or cerebral infarction) and/or necrotizing enterocolitis (NEC >grade 1).