Many things related to fetal monitoring in labour have been introduced because they seemed like a good idea, but never properly evaluated to determine whether they work (like “Fresh Eyes” checks, and central fetal monitoring). There is increasing recognition that one of the reasons for poor outcomes when CTG monitoring is used is not realising the heart rate being recorded is that of the woman and not her fetus. Many professional guidelines now recommend simultaneous and continuous recording of the woman’s heart rate. It seems like a good idea, but does it work? Unlike other aspects of practice relating to fetal heart rate monitoring in labour, researchers have recently set out to answer this question (Tarvonen et al, 2024).

How was the research done?

Routinely collected information about women who gave birth in one district in Finland between 2005 and 2023 was examined. The women were pregnant with one baby who was head first, 37 weeks pregnant or more at the time of birth, had a non-instrumental vaginal birth, had CTG monitoring throughout labour, and had blood gas testing of the umbilical cord blood. Both external Doppler sensors and fetal spiral electrodes were used, but there were no noninvasive fetal ECG monitors, ST analysis, or computer interpretation of the CTGs. Fetal blood sampling was in common use. Maternal heart rates (when they were measured) were recorded with a pulse oximeter or via a Doppler sensor built into the tocodynanometer sensor (some fetal monitors offer this in their design). All the CTG recording were stored electronically in a system known as Milou, that also has to capability to act as a central fetal monitoring system. Whether this was used or not is not explained in the paper.

The authors were specifically interested in finding out whether there were differences in the pH or base excess levels in cord blood, Apgar scores at five minutes of age, the use of intubation for resuscitation, neonatal encephalopathy, or death in the first 4 weeks of life. They used statistical approaches to reduce the chance that something other than the type of monitoring used was associated with the outcome. Specifically – they corrected for parity, BMI, diabetes, postterm pregnancy, maternal age >35, preeclampsia, fever, smoking, fetal sex, fetal growth restriction, small or large for gestational age, meconium stained liquor, induction and augmentation of labour, epidural use, year of birth, and shoulder dystocia.

What did they find?

213,789 women met the criteria for the research. 38% had fetal heart rate monitoring with a Doppler sensor for their CTG, 29% used a Doppler sensor AND had maternal heart rate monitoring, and 33% used a fetal spiral electrode. The outcomes of interest were compared between these three groups. Women who were monitored with Doppler fetal heart rate assessment alone compared to women who also had maternal heart rate monitoring were statistically more likely to have a baby with neonatal encephalopathy (1.4 per 1,000 births vs 0.9 per 1,000), cord blood pH of <7.0 (4 per 1,000 vs 2 per 1,000), the use of intubation for resuscitation(5 per 1,000 vs 4 per 1,000) , or who was admitted to the nursery for neonatal asphyxia (23 per 1,000 vs 20 per 1,000). Similar differences were also seen when Doppler fetal heart rate monitoring was compared with the use of a fetal spiral electrode: neonatal encephalopathy (1.4 per 1,000 vs 0.7 per 1,000), cord blood pH of < 7.0 (4 per 1,000 vs 2 per 1,000), intubation (5 per 1,000 vs 4 per 1,000), and admission (23 per 1,000 vs 17 per 1,000). Death rates were not significantly different in either of these two comparisons, but the study size was not large enough to provide reliable statistics for this outcome.

This begs the question – is it better to add maternal heart rate monitoring to external Doppler fetal heart rate monitoring, or to skip maternal heart rate monitoring and switch to a fetal spiral electrode? The researchers looked at this. There were no significant differences in the rates of neonatal encephalopathy, cord blood pH < 7.0 or intubation, although the rate of admissions was slightly lower with fetal spiral electrode use (3 fewer admissions per 1,000 births).

So what does this mean?

For women at term, with one head first baby, who make an informed decision to use CTG monitoring for labour, adding simultaneous recording of the woman’s heart rate to the CTG was associated with better outcomes for the baby. Switching from external (Doppler) monitoring to internal (fetal spiral electrode) monitoring also improved outcomes but only performed better than adding maternal heart rate tracing to external monitoring for reducing admissions to the nursery, and only by a small amount.

These findings may or may not apply to women in preterm labour, with multiple pregnancy, or with babies presenting breech – we don’t know. The study was retrospective, so it remains possible that there might be other reasons for the differences than the type of monitoring used. A randomised controlled trial would be a more reliable approach to answering the question, and is hopefully more likely to be done now there are preliminary findings suggesting that further investigation is worthwhile.

It seems reasonable to add that for women who chose intermittent auscultation in labour, careful attention to be sure that what is being heard really is the fetal heart rate is also important. I’m not aware of any research that has investigated how often maternal heart rate is confused for fetal heart rate when intermittent auscultation is being used. My gut feeling from my previous clinical practice is that it is possibly less common than mistaking maternal heart rate for fetal with CTG use. I’d love to know what your thoughts are about this.

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References

Tarvonen, M., Markkanen, J., Tuppurainen, V., Jernman, R., Stefanovic, V., & Andersson, S. (2024, Apr). Intrapartum cardiotocography with simultaneous maternal heart rate registration improves neonatal outcome. American Journal of Obstetrics & Gynecology, 230(4), 379 e371-379 e312. https://doi.org/10.1016/j.ajog.2024.01.011 

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Categories: CTG, EFM, New research, Perinatal brain injury, Perinatal mortality

Tags: fetal scalp electrode, FSE, maternal heart rate, Neonatal encephalopathy, pH, pulse oximetry