What’s the evidence on optimal cord clamping?
We’ve known for many years that there are many advantages to leaving the umbilical cord intact for a few minutes after birth.
On this page, I share a few of the key studies that I have highlighted and written about in this area, and links to other relevant blog posts.
Turning it around
In fact, it may be more accurate to turn this around and explain that the modern obstetric practice of clamping and cutting the umbilical birth immediately after birth is dngerous.
And it is.
Clamping and cutting the cord too early (including with shoelaces – please don’t ever do this) can deplete a baby’s iron stores and be detrimental to their health.
In premature babies, early clamping and cutting of the cord leads to a lower chance of survival. Evidence shows that optimal cord management reduces death in preterm babies by nearly a third.
This is important information for parents, caregivers, birth workers and others.
Birthing Your Placenta
“Another thing very injurious to the child is the tying and cutting of the navel string too soon: which should always be left till the child has not only repeatedly breathed but till all pulsation in the cord ceases. As otherwise the child is much weaker than it ought to be, a portion of blood being left in the placenta which ought to have been in the child.” (Darwin 1801).
Let’s start with an adapted excerpt from Birthing Your Placenta: the third stage of labour, in which Nadine Edwards and I explain the evidence on many aspects of the birth of the placenta for those wishing to better understand and make informed decisions about this element of birth.
What used to happen?
In days gone by, it would probably have been unnatural for a mother to sever the umbilical cord immediately, although common sense suggests that the timing and method of cord severing would be dependent on the circumstances and context in which a woman birthed.
We can’t go back in time to see how our ancestors severed their babies’ cords, but we know from the animal kingdom that there are a range of behaviours.
In more recent times, maternity practitioners adopted the practice of clamping and then cutting the baby’s umbilical cord soon after birth, thus separating the baby from its mother. But the nature and timing of this practice has been questioned and reconsidered in turn.
There hasn’t been much interest in studying what happens in women’s and babies’ bodies if birth is not interfered with. Because of this, much of what we know about the advantages of waiting has come out of research studies looking at the disadvantages of immediate cord clamping.
This is sadly not a unique situation. There are many other situations in maternity care where normal physiology is not well understood and in which we may well be causing more harm than good by interfering on a routine basis. (Edwards and Wickham 2015).
Evidence of the advantages of patience
The transfer of the blood that has been circulating in the placenta in the moments after birth is the main reason that it is important to allow time before clamping and cutting the baby’s cord.
Many practitioners are aware that the baby needs to be able to access its full complement of blood in order to support lung expansion and additional blood volume requirements from the placenta which occur as the first breaths of air are taken.
If the cord is clamped immediately at birth, blood from the placenta cannot flow through it and this blood therefore cannot be used to support the process of lung expansion and respiration.
Blood then has to be ‘borrowed’ from the rest of the baby’s circulation in order for its lungs to become fully functioning, even though the baby’s other vital organs also need blood to function fully and optimally (Mercer et al 2008, Mercer & Erickson-Owens 2010). (Edwards and Wickham 2015).
Myriad reasons
We are only really beginning to discover the myriad reasons why babies need to be able to access their full complement of blood before we interfere with the supply by clamping and cutting the cord.
Our knowledge of this area has increased fairly rapidly over the past few years, although we still have a lot to learn.
In 1974, Yao and Lind found that, when a baby received its full quota of blood, it was better able to maintain its haematocrit levels (ratio of red blood cells to total volume of blood). In the past, commentators knew that this quota of blood was important (Inch 1983) but it is only more recently that we have come to understand the implications of early cord clamping more fully.
The research in this area has now become more widely known and incorporated into practice. A number of studies have shown that allowing the cord to remain intact for a period of time confers significant advantages to the baby (Mercer & Erickson-Owens 2010, Hutchon 2012, Bhatt et al 2013, McDonald et al 2013, Mercer & Erickson-Owens 2014, Hooper et al 2015). (Edwards and Wickham 2015).
The RCOG scientific impact paper (2015)
In 2015, an updated RCOG scientific impact paper added further support for delayed cord clamping.
It warned that immediate cord clamping can be harmful to babies by negatively affecting their blood flow and reducing iron stores. The latter is associated with neurodevelopmental delay in babies.
The paper also acknowledged that early cord clamping, which has been a mainstay of medical management of the birth of the placenta for several decades despite a lack of evidence to support such interference, can negatively interfere with the baby’s transition from fetal to neonatal circulation.
The paper described our current understanding of what happens physiologically in the baby’s first minutes of life, and explains why immediate cord clamping can be problematic:
“At birth, the umbilical circulation slows and pulmonary vascular resistance falls, rapidly increasing pulmonary blood flow. This is the beginning of the transition from the fetal to the neonatal circulation. Continued flow in the umbilical vein and arteries at birth may be part of the physiological mechanisms assisting the baby as it makes this transition. Immediate cord clamping may restrict the baby’s ability to deal with the transition from the fetal to the neonatal circulation. While most healthy babies at term adapt without major consequences, for those born preterm or with their cardiorespiratory circulation already impaired, there may be an impact on clinical outcome. A brief delay in cord clamping will increase the baby’s blood volume. With a longer delay there may be other advantages, such as better cardiorespiratory transition and more stable blood pressure, and these might occur even with no further change in net blood volume.”
In the report, delayed (or deferred, as the RCOG have chosen to term it, claiming that “the previously used ‘delayed’ … might be felt to imply later than ideal”, although optimal might be an even better term) cord clamping is defined as being at least two minutes after birth, although women who want the cord to be left intact for longer than this should be supported in this.
More recent evidence suggests that a longer time frame may be preferable, as I will discuss below.
The full report can be found here and the BMJ also reported on it.
And now?
Our current understanding continues to be that allowing the cord to remain intact helps a baby to establish their breathing and circulation, which is particularly advantageous for babies who are compromised or born prematurely (Mercer & Erickson-Owens 2010).
Allowing the cord to remain intact can lead to a reduction in breathing difficulties and less need for oxygen, ventilation and blood transfusion (Mercer 2001).
Other benefits include an improvement in cardiac (heart) function (Bhatt et al 2013, Hooper et al 2015), an increase in the baby’s iron stores (Chaparro et al 2006, Andersson et al 2011) and neurological advantages (Hutchon & Wepster 2014).
We know that later cord clamping can lead to a baby receiving millions more stem cells (which have healing qualities) than if the cord is clamped and cut early (Mercer & Erickson-Owens 2010).
Later cord clamping can also reduce the likelihood of severe infection (also known as sepsis) in pre-term babies (Mercer & Erickson Owens 2006, Mercer & Erickson Owens 2010). Hutchon (2016b) suggested that the intervention of immediate cord clamping may cause some babies to need to be resuscitated.
Other studies show that babies whose cords are clamped earlier experience disadvantages. Mercer et al (2008) note that babies who experience immediate cord clamping are likely to have hypovolaemia (too little blood volume) and suggest that this can lead to the release of substances called inflammatory cytokines, which are associated with cerebral palsy. (Edwards and Wickham 2015).
Reviews of the Evidence
These benefits are summarised in systematic reviews and acknowledged in reviews looking at the ‘management’ of the birth of the placenta.
In 2010, the Cochrane review comparing active management with physiological placental birth noted that about 20 per cent of a baby’s blood volume is lost when the cord is clamped early (Begley et al 2010).
The 2019 Cochrane review on this topic also cited multiple concerns about the detrimental effects of early cord clamping.
A 2018 systematic review “…provides high-quality evidence that delayed clamping reduced hospital mortality, which supports current guidelines recommending delayed clamping in preterm infants.”
A 2019 Cochrane review on the timing of cord clamping confirmed that, “Delayed, rather than early, cord clamping may reduce the risk of death before discharge for babies born preterm.”
This is also acknowledged in reviews on cord clamping, for instance where McDonald et al (2013) note Mercer’s (2001) revelation that “…placental transfusion can provide the infant with an additional 30% more blood volume and up to 60% more red blood cells.”
The benefits of higher iron stores are experienced for several months after birth, even if the cord remains intact for only 1-3 minutes after birth (McDonald et al 2013).
A 2023 study again confirmed that, “In neonates born via cesarean section, DCC [delayed cord clamping] resulted in improved hematocrit levels by 72 hours compared to UCM [umbilical cord milking]. DCC results in better placental transfusion.”
Delaying cord clamping for six minutes is safe
One of the challenges faced by those researching this area is that reviews necessarily include older evidence, which can mean the results are confusing or misleading. So it can also be helpful to look at the results of well-conducted and recent trials.
One example is this 2019 study which showed that delayed cord clamping after three minutes was associated with an improvement of the overall neurodevelopment assessed at 12 months of age, as compared to infants in the group with cord clamping within one minute.
And in 2021, another important study showed that it is safe to wait 6 minutes after birth, even when an oxytocic drug is given to assist with the birth of the placenta. Here’s a post I wrote about that:
Gathering the evidence
In 2021, expert researchers in this field brought together the evidence in this area in an important paper.
In Cord Management of the Term Newborn, Ola Andersson and Judith Mercer summarise the key points from the available evidence.
- “Keeping the umbilical cord intact by delaying cord clamping for at least 3 minutes improves iron stores during infancy and supports health and development for the growing child. In preterm infants, delayed cord clamping reduces mortality by approximately 30%.
- Many midwives prefer to delay cord clamping until pulsations cease or until the placenta is ready to deliver and experience good results.
- To warn for risk of jaundice and need for phototherapy after delayed cord clamping is not evidence based.
- A multidisciplinary approach is critical to implement guidelines, training, and education with scheduled audits to increase compliance with delayed cord clamping.
- Intact cord resuscitation has been practiced for centuries at midwifery births, and has shown physiologic improvements in animal and human trials.” (Andersson & Mercer 2021).
The paper covers everything from the physiology of transfusion to the most recent evidence about the optimal timing of cord clamping. Andersson & Mercer (2021) discuss giving uterotonics (RCT evidence showed no negative effects when given 3 minutes after birth). They describe optimal cord clamping at caesarean section and cord milking. The remainder of their paper is a comprehensive summary of the evidence in every area related to optimal cord clamping.
Why this paper is still important
This summary continues to be really important, as it explains the history of this area and summarises the current evidence.
“Leaving the umbilical cord intact after birth has ensured our survival for millennia … In the mid twentieth century, with the advance of modern medicine, delayed [cord clamping] CC was replaced with the efficiency and expediency of immediate CC without testing for its safety. Practice was guided by expert opinion and delayed CC at birth was discarded from mainstream practice.” (Andersson & Mercer 2021).
So-called “expert opinion” is responsible for causing harm to women, babies and families in many other areas of maternity care. I’ve written about several other examples of this in my books. So it’s vital that we celebrate, share and cite papers like this one, which are based on scientific evidence and not the opinion, convenience or bias held by those who seek to control women and birth.
How to find out more
If you’d like to know more about this and related areas, I have an information hub offering blog posts and articles related to the birth of the placenta, which includes optimal cord clamping.
About the Author: Dr Sara Wickham is an author, speaker, and researcher specialising in pregnancy, birth and maternity care. Her work focuses on evidence-based, woman-centred information and informed decision-making, drawing on more than 30 years of midwifery knowledge and experience.
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