I have been having a very enjoyable time poking about in old research as I write a new course. I had been aware of a randomised controlled trial published in 1959 (Walker) as it appears as the only paper in a Cochrane review that I have read (Hofmeyr &Kulier, 2012), and finally got my hands on the original paper. Both the review and the trial set out to demonstrate whether responding to “fetal distress” with early intervention, rather than waiting for some other indication (like obstructed labour or infection), improved outcomes for the baby with an acceptable complication rate for women. This trial predated CTG monitoring – so it acts as a sort-of-replacement to answer the question of whether using intermittent auscultation can improve outcomes. The trial found that there was no change in perinatal mortality between the group with early intervention and those without, but a higher rate of caesarean section, forceps, and symphysiotomy* in the early intervention group.
Meconium and “fetal distress”
There’s an interesting table in the original paper and I have reproduced it below. All the women included in this trial had a diagnosis of “fetal distress” – specifically either meconium stained liquor, or an alteration in the fetal heart rate (under 110 bpm, over 160 bpm, or “persistent irregularity” – I suspect this relates to repeated decelerations in current terminology). The table provides insights into which indicator was the stronger marker for perinatal loss (death of the baby during labour or soon after). When meconium staining was present, 9.8% of babies died#. When the fetal heart rate pattern was normal (by the standards of the day) and meconium-staining was present, 9.1% of babies died – essentially the same rate of deaths.
Take away number 1 from this table is that a normal heart rate pattern when meconium is present should NOT be ignored, as it was a marker for a poor outcome.
The other side of the table is interesting too. There are no cases in the clear liquor + normal heart rate box as this would mean there was no “fetal distress” and this excluded women from the study. Of the 78 women who had an abnormal fetal heart rate AND clear liquor, the mortality rate was 2.6%. The study author said that this was the same as the rate seen in their hospital for women without fetal distress.
The second take-away from this table is that an abnormal heart rate in the presence of clear liquor was no better at predicting outcomes than a NORMAL heart rate pattern in the presence of clear liquor.
So – this research showed that you could basically ignore (or not listen to) the heart rate, and get a reliable indicator that there was a high, or low, chance of a poor outcome based just on the presence or absence of meconium in the liquor. Now clearly, obstetrics ignored that important bit of information and continued to develop the CTG machine. (Sigh.)
| Heart rate pattern | Meconium-stained liquor | Clear liquor | ||
|---|---|---|---|---|
| No of cases | Perinatal Loss | No of cases | Perinatal Loss | |
| Normal | 406 | 37 (9.1%) | – | – |
| Slow | 159 | 20 (12.6%) | 53 | 2 (4%) |
| Slow and irregular | 25 | 2 (8.0%) | 22 | 0 |
| Fast | 31 | 2 (6.4%) | 3 | 0 |
| Fast and irregular | 1 | 0 | 0 | 0 |
| Total | 622 | 61 (9.8%) | 78 | 2 (2.6%) |
Does this still apply?
Sixty-six years later, here in 2025, and with a mountain of research and experience with heart rate monitoring, does this message that meconium stained liquor is an important sign still apply? Not really. The role of meconium has shifted from being an independent marker for a poor outcome, to an indication for continuous CTG monitoring. If there is meconium and the heart rate pattern is normal, current guidelines (at least to the best of my knowledge) do not recommend further fetal assessment or intervention.
A recent retrospective trial examined the effectiveness of a computer interpretation algorithm for CTG interpretation (Menzhulina et al, 2025). They looked at whether analysing the CTG on its own (using known features such as baseline, accelerations, and decelerations) or whether adding in clinical data as well, provided better predictions of which baby would be born with a cord blood pH of less than 7.05. Digital CTGs from 1,264 women with known clinical histories and birth outcomes were put into the computer model.
Of the babies born with severe acidaemia, 32% had meconium stained liquor while only 19.1% of babies without acidaemia did – a statistically significant difference. When the researchers added the woman’s age, and whether fetal growth restriction, gestational diabetes, or a hypertensive disorder were complicating the pregnancy, to the information from the CTG, there was no change in the ability of the computer program to detect severe cord acidosis. They might as well have just used the CTG alone.
But when meconium-staining of the liquor was added to the things the computer was looking out for – the ability of the algorithm to correctly predict severe cord acidosis was much improved.
What does this mean?
We ignore other markers for low oxygen levels and a poorly functioning placenta at our peril. False negative results with CTG use (where the heart rate pattern is interpreted as normal but the baby is born with a health issue related to low oxygen levels) are not particularly common but they have been an ongoing problem throughout the history of CTG use. Choosing to consider meconium as a reason to recommend CTG use, and not as an important red flag in itself, is potentially dangerous.
The decision to focus research and development efforts on heart rate patterns rather than meconium, was financially lucrative for obstetric researchers and technology developers. Would routinely recommending caesarean or instrumental birth at the moment that meconium-stained liquor is detected produce better outcomes than putting the CTG on? We do not know because that question has not ever been addressed in research.
The decision to prioritise information from the fetal heart has cost us 60 years of knowledge development. It isn’t too late. Rather than spending more time and money on new shiny CTG machines, guidelines, and education programs, we have the opportunity to look for other clinical markers of poor outcome and to test whether using these and NOT the heart rate, might finally provide the missing link to making substantial reductions in poor perinatal outcomes. Shall we do it?
* Symphysiotomy is a surgical procedure to cut the joint at the front of the pelvis. This increases the size of the pelvic outlet. Prior to safe caesarean section it was used (often along with forceps birth) to get the baby born faster. It is only used in extremely exceptional situations in current maternity practice.
# This was 1959 Durban, Africa. The mortality rates here are MUCH higher than in modern practice. Please do not assume that one in ten babies with meconium-stained liquor, born in 2025, will die.
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References
Hofmeyr GJ, Kulier R. Operative versus conservative management for ‘fetal distress’ in labour. Cochrane Database of Systematic Reviews 2012, Issue 6. Art. No.: CD001065. DOI: 10.1002/14651858.CD001065.pub2.
Menzhulina, E., Vitrou, J., Merrer, J., Holmstrom, E., Amara, I. A., Le Pennec, E., Stirnemann, J., & Ben M’ Barek, I. (2025, Jan 29). Integration of clinical features in a computerized cardiotocography system to predict severe newborn acidemia. Eur J Obstet Gynecol Reprod Biol, 307, 78-83. https://doi.org/10.1016/j.ejogrb.2025.01.030
Walker, N. (1959, December 5). The case for conservatism in management of foetal distress. British Journal of Medicine, 2(5161), 1221-1226.
Categories: CTG, EFM, History, IA, New research, Perinatal mortality, Stillbirth
Tags: acidosis, cord blood, fetal distress, Meconium, pH
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