Birth Small Talk

Talking about birth

Noninvasive fetal ECG – how does it compare with standard CTG?

One area of technology and research development in the fetal heart rate monitoring arena is the potential for long-term at-home antenatal CTG monitoring. I have written about my concerns with this before. Non-invasive fetal ECG monitoring (the wireless and beltless option I wrote about last week) is being considered as a possible option for home use (called remote, or continuous, fetal monitoring).

What’s new?

Researchers from St George’s in London have recently reported a pilot study (Liu, et al., 2023). They compared noninvasive fetal ECG with computerised CTG (using the Dawes-Redman criteria for computer interpretation) for antenatal CTG monitoring in women considered to have a high-risk pregnancy. (The authors said “requiring CTG monitoring” but you all know how I feel about that terminology…) Indications for CTG monitoring included reduced fetal movements, prelabour membrane rupture, post-maturity, fetal growth restriction, hypertension, and others. 285 women, all with singleton pregnancies, agreed to participate. The mean gestational age was 37 weeks.

Each woman had both computerised CTG and noninvasive fetal ECG monitoring performed simultaneously during a Day Assessment Unit visit, for at least 40 minutes. The goal of the research was to compare the quality of the fetal heart rate trace from the two monitoring devices. The specific noninvasive technology used was the “femom” device. There’s a photo of it in the paper – and the paper is free to access – click on the link in the reference list. Women were asked to apply the adhesive electrode pads themselves to check this is a realistic choice in the at home setting. Only data from the computerised CTG recording was used in clinical decision-making. This was achieved by displaying the “uncleaned” ECG data containing both the maternal and fetal signals, so the fetal heart rate could not be seen.

What did they find?

The signal loss rate (the percentage of time when no fetal heart rate can be calculated from the data) was lowest with computerised CTG (1%) and was 17% with the noninvasive ECG system (using the best performing processing protocol). Signal quality from both the computerised CTG and noninvasive fetal ECG improved with increasing gestational age. Lower body mass index and fewer fetal movements during the trace was linked to better signal quality for computerised CTG but had no impact on signal quality with noninvasive fetal ECG.


If the goal is to have near-continuous recording of the fetal heart rate, then there is still some way to go with noninvasive fetal ECG technology. If the goal is long-term monitoring with periods where the trace is good enough for clinical use, noninvasive fetal ECG is probably good enough as it stands. It has the advantage of not transferring energy to the fetus (unlike the Doppler technology used in standard CTG monitoring) and therefore avoids the safety concerns associated with this.

Despite the title of the paper including the word “ambulatory”, the authors don’t describe whether women were semi-supine and at rest for the duration of the period of monitoring (I suspect so), or upright and active. Before shifting to long-term at-home use, this needs to be assessed as it is possible the sensors may not perform as well under those circumstances, or they may actually prove superior to standard CTG monitoring. Electrical interference was an issue with the noninvasive fetal ECG and I am curious about how that would translate into the home environment. Will everyday appliances like microwaves, vacuum cleaners, or an iPad resting on the belly interfere with the signal?

Many questions remain before noninvasive fetal ECG is fit for purpose in the home environment. It is great to see researchers starting to assess it before it becomes commonplace.


Liu, B., Thilaganathan, B., & Bhide, A. (2023, May). Effectiveness of ambulatory non-invasive fetal electrocardiography: impact of maternal and fetal characteristics. Acta Obstetrica et Gynecologica Scandinavica, 102(5), 577-584. 

Categories: antenatal CTG, CTG, EFM, New research

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2 replies

  1. But what is the point? Who benefits apart from the tech manufacturers.


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