Updated: Feb 17, 2021
Nuchal cord - the umbilical cord round the baby's neck at birth is a common scenario which occurs in approximately 20-30% of births (Hutchon, 2013).
So, it's unsurprising that this is a subject I am regularly asked about; particularly in relation to optimal and delayed cord clamping.
Indeed it seems that management of a nuchal cord varies from practitioner to practitioner. Student midwives often describe their concern when births with a nuchal cord are mismanaged without evidence.
I am therefore going to give you a very brief run down of the evidence and look at the physiology of what's occurring at birth including placental, umbilical cord and neonatal physiology.
This topic is something I regularly discuss at midwifery conferences and one that will be covered in a module in the upcoming BloodtoBaby course 'Bedside stabilisation with and intact placental circulation'.
Quick fire physiology
Compression of the umbilical cord through nuchal cord and various other birth scenarios can cause reduction of blood (oxygen/nutrients) to baby.
This is due to the structural physiology of the soft walled umbilical vein which can be easily compressed due to the low venous pressure. The harder, muscular umbilical arteries are not affected in the same way as the baby’s heart is pumping 40% of its combined output through the umbilical arteries at high pressure (Mercer, Skovgaard, Peareara-Eaves & Bowman, 2005). The umbilical arteries continue to move carbon dioxide and waste products from the fetus. In simple terms, when the umbilical vein is regularly occluded, there is a net transfer of blood from the fetus to the placenta.
Dependant on the severity of cord compression babies tolerance to labour may be reduced. In acute cases chemical adaptations of the fetal blood may cause degrees of acidaemia which could in chronic cases lead to acidosis and a hypoxic baby. During this time before birth the baby makes adaptations, fetal movements are reduced as non essential components are sacrificed - the reduced blood volume is used to protect the babies central circulation - the heart and brain.
During the second stage of labour the vaginal wall pressure also acts to ensure the central circulation is perfused, just as antishock garments help in the management of maternal haemorrhage in low income countries (Mercer & Erickson-Owens, 2014). However, once baby is born, the peripheral circulation opens up and because baby only has a limited supply of blood due to the cord compression, it’s usually born flat with lack of tone and respiratory effort.
The baby is hypovolemic - there is not enough blood to perfuse the lungs and brain.
It is vital that these babies are allowed placental transfusion; this supports an increase in blood volume (oxygenated) which can then provide and supply the brain and lungs. The baby won’t breathe and cry until the respiratory centre in the brain is activated; perfused with oxygenated blood.
In an ideal world, all compromised babies would be resuscitated on an intact cord. So, whilst initiating the Newborn Life Support resuscitation algorithm - starting with stimulation, thermoregulation and if needed inflation breaths to aerate the fetal lungs, the placental circulation can ensure the redistribution of blood to the baby.
It's worth noting that the opened vascular system of the lungs in connection with aeration, requires a considerable amount of blood (Niermeyer & Velaphi, 2013).