Fetal monitoring guidelines around the world recommend CTG use in labour when women are considered to be a higher risk for a bad outcome for the baby that is linked to low oxygen levels in labour. Regular readers of my blog will have seen me write repeatedly about the lack of great evidence to back this up. There’s no compelling research showing better outcomes with CTG use for women planning vaginal birth after caesarean (VBAC), with gestational diabetes, or with a higher body mass index. Back in 2019, I published a paper bringing together all the research about women considered to be a high risk, and found no evidence that CTG monitoring improved long term outcomes. (You can watch Melanie the Midwife’s excellent summary of the paper here.)
But surely it must work for someone???
Maybe it does! Dr Melanie Jackson (Aka @Melaniethemidwife) and I got together recently and recorded a podcast where she asked me that question. You can head to Mel’s website to listen to it. This post sets out the details of what we spoke about in the podcast.
As I pointed out, the majority of the research that has been done has combined women with a range of different risk factors into the one big pile, and compared outcomes with CTG use and with intermittent auscultation for ALL the women in that one big pile. This research makes it impossible to look at the findings to see whether, for example, women with pre-eclampsia do better with CTG use, while women with a small fetus do better with intermittent auscultation. But when you put those groups of women together the overall benefits cancel out.
So you need to do research where all the women have the same risk factor. Three randomised controlled trials have done this. They were all small (too small to provide answers to the questions they were asking) and one has never been published (but the numbers are included in the Alfirevic et al. 2017 Cochrane review). The trials looked at:
- Preterm labour (Luthy et al., 1987, with long term data reported in Shy et al, 1990) – finding no difference in mortality rates, seizure rates, vaginal birth rates, caesarean section rates, but a 254% increase in cerebral palsy when CTG monitoring was used.
- Meconium stained liquor (unpublished but included as Pakistan, 1989 in Alfirevic et al., 2017) – finding no difference in mortality rates, caesarean rates, and a 56% lower vaginal birth rate with CTG use. They didn’t look at seizures or cerebral palsy.
- Vaginal birth after caesarean section (Madaan & Trivedi, 2006) – finding no difference in caesarean and vaginal birth rates. There were no deaths in the trial, and they didn’t look at seizures or cerebral palsy.
It remains possible that there is a group of women who get great benefit from CTG use, but we simply have not done the right research to know who they are.
Here’s who I think CTG monitoring might be useful for…
The largest head to head comparison of CTG monitoring with intermittent auscultation in a randomised controlled trial was the Dublin trial (MacDonald et al., 1985). This was the only one of the eleven trials to show a benefit from CTG use. That benefit was a reduction in neonatal seizures – falling from 41 per 10,000 births with intermittent auscultation to 18 per 10,000 births with CTG use. This means for every 435 women using CTG monitoring rather than intermittent auscultation, there would be one fewer babies having seizures. But that doesn’t tell us which women were benefitting from CTG use and which ones were not.
There is a clue hidden deep in the paper, and not actually commented on by the authors, that provides information about which women were benefitting and which were not. In table 5, we are told how many women in each arm of the trial were using oxytocin in their labour. In table 14 they given the numbers of babies who had seizures according to whether oxytocin was being given or not. By combining the information from the two tables and with a little bit of research maths I came up with the following table –
| Oxytocin use? | CTG monitoring | Intermittent Auscultation |
|---|---|---|
| No | 15 per 10,000 | 15 per 10,000 |
| Yes | 36 per 10,000 | 160 per 10,000 |
You don’t need to be a statistics whizz to be able to see that when oxytocin was NOT in use, the type of fetal monitoring being used made no difference to the seizure rate, which remained identical and low. But when oxytocin was used, the difference is so big you don’t need to be a statistics whizz to see that either! (It is statistically significant in case you were wondering.)
There are two things to note from this bottom line. The first is that there was a 4.4 times higher seizure rate when intermittent auscultation was used rather than CTG monitoring. The other thing to note is that adding CTG monitoring when using oxytocin was not sufficiently powerful to remove the risk of harm introduced by oxytocin. The rate of seizures was just over twice as high when CTG monitoring was used AND oxytocin was given, than when intermittent auscultation was used and oxytocin was not given. This is a powerful reminder that oxytocin can be dangerous if not used safely!
OK – so you are saying that the only evidence based indication for CTG use is when oxytocin is used, right?
Well, sort of. This is the closest that you can get to a clear sign of benefit from CTG use in ANY of the research ever done about CTG monitoring. It also makes an argument to avoid oxytocin use unless you have a REALLY good reason to give it.
But there is a but. In the research world, we talk about a thing called generalisability. What this means is that research findings only apply to places and people that are very much like the places and people where the research was done. Maternity care in high-income countries in 2024 is not at all like maternity care in Dublin in the early 1980s. (Even care in Dublin in 2024 isn’t like it was in the early 1980s…)
A paper published at the same time as the Dublin trial provides some useful insights that show what has changed (Garcia, et al., 1985). Dublin was home to an approach to labour care called “Active management of labour”. A key component of this was that each woman had constant companionship from a care provider during labour. Garcia and colleagues wrote that:
Each woman is assigned a companion, usually a student midwife, but sometimes a medical student, who remains with her throughout her labor, monitors her progress and, most importantly, encourages and supports her. Overall responsibility for the delivery suite is in the hands of a senior midwife to whom those giving immediate care will turn is they are concerned and who will, herself, seek the advice of a senior obstetrician is necessary. p. 80
Not mentioned in either paper was the use of infusion pumps to control the infusion rate. The absence of mention is because they did not yet exist. This means that the rate of delivery of oxytocin was controlled by carefully rolling the stopcock on the giving set further open or closed and counting the number of drips delivered per minute. I am sufficiently aged to have learned to do this as a medical student and it is difficult to achieve anything like the precision now available with infusion pumps.
Putting those pieces of information together means that women were alone with a student (who by definition does not have much experience), who was either feeling for contractions by hand or looking at them on the CTG, who then manually adjusted the drip rate according to the contraction rate. What could possibly go wrong! This would now be considered unprofessional practice.
So when is CTG use in labour a good idea?
There might perhaps, possibly be half an argument for CTG use for women using oxytocin for labour induction or augmentation on the basis of 40 year old research with poor generalisability. And maybe, perhaps, that also extends to the use of prostaglandins for labour induction, which were not yet invented when most of the trials were done.
But the only valid indication I can come up with for CTG use is when a woman chooses to use it, ideally after she has been provided accurate and unbiased information about what it can and can not achieve, and about the potential risks associated with its use. It really is both that simple and that complicated.
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References
Alfirevic, Z., Devane, D., Gyte, G. M. L., & Cuthbert, A. (2017, Feb 03). Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour. Cochrane Database of Systematic Reviews, 2(CD006066), 1-137. https://doi.org/10.1002/14651858.CD006066.pub3
Garcia, J., MacDonald, D., Elbourne, D. R., & Grant, A. (1985, Summer). Mothers’ views of continuous electronic fetal heart monitoring and intermittent auscultation in a randomized controlled trial. Birth, 12(2), 79-86. https://doi.org/10.1111/j.1523-536x.1985.tb00943.x
Luthy, D. A., Shy, K. K., van Belle, G., Larson, E. B., Hughes, J. P., Benedetti, T., Brown, Z. A., Effer, S., King, J. F., & Stenchever, M. A. (1987, May 01). A randomized trial of electronic fetal monitoring in preterm labor. Obstetrics & Gynecology, 69(5), 687-695. https://www.ncbi.nlm.nih.gov/pubmed/3554055
Madaan, M., & Trivedi, S. S. (2006, Aug). Intrapartum electronic fetal monitoring vs. intermittent auscultation in postcesarean pregnancies. International Journal of Gynecology & Obstetrics, 94(2), 123-125. https://doi.org/10.1016/j.ijgo.2006.03.026
Shy, K. K., Luthy, D. A., Bennett, F. C., Whitfield, M., Larson, E. B., van Belle, G., Hughes, J. P., Wilson, J. A., & Stenchever, M. A. (1990, Mar 01). Effects of electronic fetal-heart-rate monitoring, as compared with periodic auscultation, on the neurologic development of premature infants. New England Journal of Medicine, 322(9), 588-593. https://doi.org/10.1056/NEJM199003013220904
Categories: CTG, EFM, History, Perinatal brain injury, Perinatal mortality
Tags: BMI, caesarean section, decision making, diabetes, Dublin, Meconium, oxytocin, preterm, VBAC
5 replies ›
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- Myth busting #1: There is no alternative to the CTG – Birth Small Talk
- Essential Guide To Waterbirth – Birth Journeys with Leah | Antenatal Courses in Leeds
Birth Small Talk 
Thanks so much Kirsten. I’ve often wondered about the claim that CTG prevents neonatal seizures, where and why. A wonderful piece of detective work on your part. So you could say that syntocinon doubles the risk of seizures when CTG is used and multiplies the risk tenfold when it isn’t.
I also wonder why it is thought useful to measure a contraction by what is happening at one point on the skin above an organ with a surface area at least 100 times the area of the transducer. But of course we do need CTG because women don’t know when contractions are happening and midwives have no way of telling when a woman is having one!
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That’s what I thought! When I saw your (broken) link to when CTG was a benefit, I thought, “Wait, did I miss something?” But I see that I did not. You do wonderful work, Kirsten. I only wish there were some way to amplify it!
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Thanks Catherine – and apologies for the broken link in the email!
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