Nuchal Cords: the perfect scapegoat

intervention physiology

This was the first blog post I wrote on MidwifeThinking in 2010. The content is based on part of a literature review I carried out for my PhD thesis. I have also written a couple of journal articles on the topic (see my publication list), and had my work cited in guidelines and textbooks. This new version of the blog post includes updated research.

Around 30% of babies are born with the umbilical cord around their neck. A nuchal cord is also more likely with increasing gestation, one study found an incidence of 12% at 24 weeks and 37% at term [1]. If a nuchal cord does not occur in pregnancy, it can occur during labour. As the baby rotates through the pelvis, they can wind the cord around their neck.

The nuchal cord has become the perfect scapegoat because it lays blame on the mother/baby rather than the care provider/system. This has resulted in fear about nuchal cords becoming embedded within our culture. When I read a story about an unexpected birth outside of the hospital, it often involves a nuchal cord. The story is about how lucky the baby was to survive the dangers of a nuchal cord away from the experts who can manage such a complication. I have also heard many birth stories where complications were unfairly blamed on the presence of a nuchal cord. Very occasionally, a nuchal cord causes complications, but in the vast majority of cases, it is a normal variation.

Before I tackle some of the misinformation and look at the research—some quick anatomy and physiology: The umbilical cord is covered in Wharton's jelly and coiled like a telephone wire. This protects the three blood vessels from the kind of stretch and compression involved in being attached to a mobile baby. The umbilical cord is also long enough (average 55cm) to be comfortably wrapped around the neck with plenty of leftover length. Essentially, the umbilical cord is 'designed' to be wrapped around the neck (and body) without causing a problem.

A nuchal cord during pregnancy

A nuchal cord in pregnancy very rarely becomes a complication. One of the problems with the research on this topic is that studies often combine nuchal cords with different types of complex cord entanglement and cord knots in the findings. When studies look at 'simple' nuchal cords, there is no association with morbidity or mortality for the baby [2]. Unfortunately, some babies die before labour begins, and there is often no known cause, which can add to the devastation for the family. When these babies are born, they are often found to have the cord around their neck (like a 3rd of all babies). Although I can understand the need to find a reason and to pick the obvious, I don't think this is helpful in the longer term. Parents need honest answers about the loss of their baby, even if the answer is 'we don't know'.

A nuchal cord during labour

Physiology

The baby is not 'held up' by a nuchal cord because the whole package – fundus (top of the uterus), placenta and cord are all moving down together (see diagram). The uterus shrinks down during contractions, moving the baby downwards, along with their attached placenta and cord. In fact, the space between the baby's neck and the placenta is shorter at the end of labour because the baby is more scrunched up.

Diagrams available here

However, when a c-section is performed for 'fetal distress' or ‘lack of progress’ during labour, the presence of a nuchal cord is often used as the reason, e.g. “your baby was stressed because the cord was around his neck” or "the cord was stopping her from moving down". The cord is unlikely to have had anything to do with any stress or lack of progress during labour. Most likely, other interventions carried out during labour led to the end scenario (in particular, the use of syntocinon). In fact, having the cord tucked around the neck can protect it from the pressure of contractions.

At the end of labour, as the baby's head moves out of the uterus and through the vagina, the cord remains loose because there is lots of 'give' in it, and it requires less length than it did at the end of pregnancy (see diagram).

Diagrams available here

A loose nuchal cord does not cause any problems. Blood continues to flow through the vessels just as it did during pregnancy and labour. Very occasionally, the cord becomes stretched and tight during this last bit of labour, just as the head is born. Either there is not enough 'give', or the cord is trapped against the pelvis by the baby's body. This may happen with a shorter-than-average cord that is wrapped around the neck a number of times. However, the baby is not 'strangled' because they are not breathing oxygen. During birth, oxygen is provided by the cord, not via the airway. While the cord is stretched and compressed, the blood vessels transfer less blood (but still some). This may result in short-term hypoxia (reduced oxygen supply), which resolves once the cord is loosened after birth and full blood flow resumes. These babies may arrive a little compromised but quickly recover - if the cord is left alone.

The photograph at the top of this post is from a case study I share in the Reclaiming Childbirth Collective Learning Library. The baby was born at home into water. His cord was tightly around his neck twice. You can see a white band on his neck where his cord had been during birth. The midwife is unwinding the cord while bringing him to the surface and into his mother’s arms. He took around 30 seconds to start breathing whilst his placental circulation re-established his blood volume and oxygenated him. His father gently blew on his face, and he took his first gasp and started crying. Unfortunately, the way in which this type of situation is usually managed (see below) can create problems. The resulting need for resuscitation is then blamed on the nuchal cord rather than what was done by the care provider.

Research

My review of the research literature [2] found that a small number of studies were unable to find any significant outcomes associated with nuchal cords. However, most studies examining outcomes related to a nuchal cord at birth identify an association with fetal heart rate abnormalities, operative delivery, lower cord pH, lower Apgar scores, and admission to special care nursery. Remember, an association is not necessarily a causation.

A number of problems arise when attempting to interpret the results of research examining outcomes associated with nuchal cords:

Reporting bias influences the findings. Greenwood and Impey [3] compared outcomes associated with a tight nuchal cord between one hospital that routinely recorded the presence of a nuchal cord at every birth and hospitals where recording was at the discretion of the birth attendant. When recording was discretionary, the presence of a nuchal cord was associated with lower Apgar scores and cerebral palsy. However, this association was absent when nuchal cords were routinely documented. These findings suggest that birth attendants are more likely to document the presence of a nuchal cord when there is evidence of neonatal compromise.
Most studies do not distinguish between a loose nuchal cord and a tight nuchal cord. Studies that do differentiate report that the association with complications is only related to tight nuchal cords.
The common practice of clamping and cutting a tight nuchal cord may be the actual cause of reported complications. A lower cord pH, lower Apgar score and admission to special care nursery may all be the result of cutting off the baby’s placental circulation. In three of the studies that differentiated between loose and tight cords, a tight cord was defined by the need to clamp and cut. The other two studies did not provide information regarding the management of nuchal cords. However, it may be assumed that at least a proportion of the cords were clamped and cut, considering that doing so appears to be common practice. So what the studies are actually reporting is the outcome for babies who have their umbilical cord prematurely cut.

The actual risks of a nuchal cord

Clamping and cutting a tight nuchal cord

Once the cord is clamped, blood flow between the baby and the placenta ceases, reducing the baby’s blood volume and oxygen supply. This makes resuscitation more necessary and difficult once the baby is born. Any delay in the birth of the baby (eg. shoulder dystocia) will further increase the risk of hypoxia. While waiting to be born, the baby has NO blood supply rather than a limited one. The damaging impact of cutting a nuchal cord is becoming commonly understood in medicine and midwifery. A policy of keeping a nuchal cord intact has been found to improve outcomes for babies [4].

For a baby with a tight nuchal cord, the worst thing you can do is clamp and cut!

Pulling and looping a loose nuchal cord

A far more common practice is pulling and looping a loose nuchal cord. Most care providers do this and I was taught to do this when I trained. However, handling the cord stimulates the umbilical arteries to vasoconstrict, reducing blood flow. Loosening the cord will usually involve some traction, which can risk tearing the cord and subsequent bleeding (from the baby) or partial detachment of the placenta. As a student midwife, I snapped a cord while looping it over the baby’s head. Luckily, my mentor clamped the ends quickly, but not before I got blood sprayed in my eyes! I later learned that babies can be born with the cord around their neck. They either birth through the loop, or they come out with it still wrapped.

Checking for a nuchal cord

If you are not going to cut or loop a nuchal cord what's the point in digging about to see if it is there? Checking for a cord interferes with the physiological process of birth [5]. It also reinforces the notion that this is a birth complication that endangers the baby rather than a common situation. Telling the woman to stop pushing and putting your fingers into her vagina can be disempowering and painful. There are also consent issues. How many care providers gain consent before carrying out this procedure?

Suggestions

Talk to parents during pregnancy about the possibility and normalcy of a nuchal cord (a third of all babies have a nuchal cord at birth).
During birth, DO NOTHING.
If the cord prevents the baby from descending once the head is born (extremely rare), use the ‘somersault technique’ (see photos in this article or this movie. However, you are unlikely to need to do this. Most babies in this situation will somersault themselves out, particularly if they are in water.
Once the baby is born, gently unwrap the cord (the mother/family can do this).
If the baby is compromised at birth encourage the parents to talk to their baby and touch their baby while the placental circulation re-establishes the normal blood volume and oxygen. If the baby requires resuscitation, do it with the cord intact.

Summary

A nuchal cord is a normal variation and very rarely causes a complication. In most cases, the complications associated with a nuchal cord are caused by care provider interventions such as pulling or cutting the cord.