Professor Susan Bewley is a professor of obstetrics with an interest in a great many things. I first became aware of her work many years ago, when I saw her writing about the potential links between the timing of cord clamping, cord blood pH testing, fetal monitoring methods, and perinatal outcomes. Susan recently challenged me to summarise the issues in a blog post – so here we go!
Setting the scene
At some point in the past, it became standard practice to quickly clamp and cut the umbilical cord after birth. This separates the baby from the placenta. This is now known as early or premature cord clamping. It is inherently un-physiological. The past few decades have seen significant work to understand the consequences of this action. I won’t go into the details but Dr Rachel Reed at Midwife Thinking covers much of this on her blog if you are interested. Suffice to say, there is now evidence this practice is harmful, particularly for preterm babies.
But what has that go to do with fetal monitoring?
Measuring outcomes that matter
When you are doing research to determine whether thing A or thing B is better, you need to answer the question – better in terms of what, exactly? In fetal monitoring research, much of the focus has been on commonly occurring, easy to measure, short term outcomes that are at least loosely associated with less common and longer-term outcomes like cerebral palsy. Casting an eye back to the early years of research about fetal monitoring reveals that Apgar scores (for example – Manley & Newman, 1973) and cord pH levels (for example Edington et al., 1975) were common outcome measures.
So what is the issue?
As Dr Melanie Jackson (aka Melanie the Midwife) recently and very eloquently explained in her podcast, the research that sits behind the decision to create Apgar scores was all done with babies who had early cord clamping. Research to determine reliable markers indicating the “need” for resuscitation in babies whose cords are left intact until placental circulation has ceased have never been developed.
While it is technically possible to collect cord blood from an intact cord (Andersson & Zaigham, 2023), all the early research done to establish what a normal cord pH level is was done with early cord clamping. It is only in quite recent times that researchers have sought to determine how to interpret cord pH results collected from an intact cord, or after a period where placental circulation has continued. Cord pH levels are lower in the first minutes after birth with an intact cord – as blood from areas of the infant’s body that had low oxygen levels prior to birth is flushed into the circulation (known as hidden acidosis) (Olofsson, 2023). The levels also change really quickly, so the precise timing of when blood is collected in relation to birth is important when considering what to call normal.
Human physiology research examining the connection between cord pH levels and clinical outcomes tends not to mention how the cord was managed around the time of birth. For example, Lissauer and Steer (1986) examined the relationship between cord pH levels and fetal heart rate patterns seen on the CTG in infants who had been resuscitated at birth. They don’t mention the timing of cord clamping at all. They found that babies with cord blood acidosis were more likely to have had a heart rate pattern considered abnormal.
They also found that birth weight was lower in the infants with abnormal heart rate patterns. Now this could be because babies who are growth restricted are less able to cope with low oxygen levels in labour. Or it might be a sign that there were differences in the timing of cord clamping. Birth weight is higher (by about 100g at term) when the cord is clamped late (Andersson & Zaigham, 2023). Maybe what is really going on here is that clinicians saw the abnormal heart rate, rushed to clamp the cord and get the baby across to the resuscitation trolley as they were expecting a need for resuscitation, and that’s why they weighed less. And maybe, just maybe, some of the clinical signs that indicated a need for resuscitation (like a slow heart rate) were due to (you guessed it!) early cord clamping.
What does that mean for the research about CTG monitoring?
I have gone back and looked at the fine print of some of the randomised controlled trials that make up the evidence base about CTG use. The first trial (Haverkamp et al., 1976, p.311) specifically said that “the umbilical cord was doubly clamped as soon as possible after birth, before the infant breathed”. The Athens trial (Vintzileos et al., 1993) makes no mention of the timing of cord clamping, but collected cord blood gases on all babies, so I think we can assume all were clamped early. The large Dublin trial (MacDonald et al., 1985) measured cord pH on only the first 1,000 births (of the 13,084 included in the trial). For these the cord was clamped “at birth” (p. 528) with no other mention of what the practice was for the other births.
My guess is that for all the infants born in all the trials, early cord clamping was used.
Here’s the thing…
Here’s the situation we find ourselves in. Early cord clamping can itself lead to worse neurological outcomes for the baby. The research we have linking outcomes like Apgar scores and pH levels both to certain heart rate patterns, and also linking these short term measures to long term outcomes seems to have used early cord clamping. The research we have about whether CTGs or intermittent auscultation works better seems to have used early cord clamping.
We have no way of knowing whether all, or some, of the poor neurological outcomes in any of this research were due to the way the umbilical cord was handled at birth or was really due to low oxygen levels in labour. Subtle differences in the timing of cord clamping between CTG use and intermittent auscultation might help explain some of the things that are difficult to explain in the fetal monitoring research – like why preterm infants exposed to CTG monitoring are 254% more likely to develop cerebral palsy than those who had been monitored by intermittent auscultation.
We need to seriously (and urgently) rethink everything we think we know about fetal and neonatal physiology that is based on research performed on infants after the very un-physiological intervention of clamping the cord before breathing has been established. The more deeply I dig into research about fetal monitoring, the less certain I am that we actually know anything we can rely on in clinical practice.
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References
Andersson, O. & Zaigham, M. (2023). Cord clamping – ‘hold on a minutes not enough, and sample your blood gases while waiting. Seminars in Perinatology, 47(4), 151739. https://doi.org/10.1016/j.semperi.2023.151739
Edington, P. T., Sibanda, J., & Beard, R. W. (1975). Influence on clinical practice of routine intra-partum fetal monitoring. BMJ (Clinical research ed), 3(5979), 341-343.
Haverkamp, A. D., Thompson, H. E., McFee, J. G., & Cetrulo, C. (1976, Jun 01). The evaluation of continuous fetal heart rate monitoring in high-risk pregnancy. American Journal of Obstetrics & Gynecology, 125(3), 310-320. https://doi.org/0002-9378
Lissauer, T. J., & Steer, P. J. (1987). The relation between the need for intubation at birth, abnormal cardiotocograms in labour and cord artery blood gas and pH values. Obstetric Anesthesia Digest, 7(2), 57. https://doi.org/10.1097/00132582-198707000-00019
Manley, J. W., & Newman, R. L. (1973). Fetal monitoring experiences in a private hospital. Missouri medicine, 70(5), 310-312.
Olofsson, P. (2023, May). Umbilical cord pH, blood gases, and lactate at birth: normal values, interpretation, and clinical utility. American Journal of Obstetrics and Gynecology, 228(5S), S1222-S1240. https://doi.org/10.1016/j.ajog.2022.07.001
Vintzileos, A. M., Antsaklis, A., Varvarigos, I., Papas, C., Sofatzis, I., & Montgomery, J. T. (1993, Jun 01). A randomized trial of intrapartum electronic fetal heart rate monitoring versus intermittent auscultation. Obstetrics & Gynecology, 81(6), 899-907. https://www.ncbi.nlm.nih.gov/pubmed/8497353
Categories: CTG, EFM, History, Perinatal brain injury
Tags: acidosis, Apgar, cord clamping, pH, Physiology
Birth Small Talk 
Thanks Kirsten for this deep dive into the association between timing of cord clamping, pH measurements and potential impacts on infant outcomes. Cord clamping and physiological management of placental birth has been a topic of interest to me for 25 years.
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Glad you enjoyed it Lois!
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