When a treatment doesn’t work at the dose administered, sometimes people increase the dose in an attempt to see if that solves the problem. It’s not usually effective. I keep an eye out for new research about fetal monitoring on a regular basis. One of the growing areas of research in the world of fetal monitoring is what is currently called continuous fetal monitoring or CFM. CFM refers to prolonged periods of monitoring during the antenatal period and is currently targeted towards women who are considered to be at high risk. It had been my intention to get around to a comprehensive review of the literature about CFM at some point for my own interest, but it seems that sometimes good things come to she who waits, as Tamber et al. (2020) have just published such a review. Most of what follows has come from their paper.
What is CFM?
CFM refers to some form of fetal monitoring, applied during the antenatal period, over a prolonged period, typically several hours, but potentially for days or even weeks – rather than the 20 to 60 minutes typically used for antenatal CTG monitoring. Two quite different forms of CFM are currently under development and being trialled – fetal heart rate monitoring and fetal movement monitoring. Let’s start with fetal heart rate monitoring.
Continuous fetal heart rate monitoring technology
As we know from CTG monitoring, it is believed that a fetus who is experiencing low oxygen supply will display particular patterns of change in the heart rate over time. Standard CTG monitoring uses Doppler ultrasound to detect movements in the fetal heart and converts this to the sound that we recognise in clinical practice. There have always been background concerns about long term use of Doppler technology for fetal monitoring, as it is known to induce heating of the tissues that lie within the line of the Doppler ultrasound beam, with little clear evidence about when too much is too much. Doppler technology has therefore been rejected as an option for CFM.
Two alternate technologies are being used for CFM instead (and in one instance both were combined within the one monitor). The first approach is to record the weak electrical signal generated by the fetal heart – known as fECG or fetal electrocardiography. To do this, sensors (between 2 and 16) placed on the woman’s abdomen record the electrical signal from both her heart and that of her fetus, then electronically remove the signal from the woman, leaving that of the fetus. The other approach uses a recording device to listen directly to the sound the fetal heart makes – known as fPCG or fetal phonocardiography. Regardless of the type of technology used, the aim is the same: to detect changes in the fetal heart rate pattern which predict which fetus is at high risk of injury so that it can be delivered early, thereby preventing death or injury to delicate tissues such as the brain.
Continuous fetal movement monitoring technology
The other form of CFM aims to track fetal movements. The theory here is that when a fetus is not receiving enough oxygen, they will limit their movements in an attempt to reduce the demand for oxygen. Again, two technology approaches are being trialed here. The first approach uses an accelerometer to detect movement – much like the step counter built into most smart phones. The other is called fVCG (confused by all these abbreviations yet? I am!) – or fetal vectorcardiography. By measuring the fetal ECG in multiple places over the maternal abdomen, comparisons between each sensor can be made, building up an electrical map of the position the fetal heart occupies. As the fetus moves, the relationship of the heart to the sensors changes, and therefore a sense of the presence of fetal body movements can be generated.
What do we know about CFM?
All of the current approaches to CFM are very much in their infancy. The research examined in this literature review focussed mostly on demonstrating that the equipment can actually detect the fetal heart rate, or movements, over a period of time (ranging from as little as five minutes to up to 23 and a half hours). Most of the studies were conducted on women with singleton pregnancies, though some included women with twin and triplet pregnancies. There is as yet no research on whether CFM improves pregnancy outcomes.
The review reported on some of the challenges of getting this technology to work. Maternal movement reduced the quality of the signal, as did the presence of contractions. Signal quality was highest at early gestations (under 24 weeks) and later gestations (after 34 weeks), with less accurate recordings obtained in between. Women who were monitored in hospital rather than at home, or during sleep, had better quality signals. Both of these relate to less maternal movement during monitoring.
I have concerns…
I’m more concerned by fetal movement monitoring as a form of CFM than by fetal heart rate monitoring. There is a body of research which demonstrates that certain heart rate patterns are associated with higher rates of poor outcome (see for example Cahill, et al, 2018). We have no equivalent research regarding fetal movement patterns, so it would be hugely challenging to attempt to make clinical management decisions on the basis of information from fetal movement monitors. The research we have to date on heightened awareness of fetal movements demonstrates no improvement in perinatal outcomes, but the use of more intervention (Bellussi et al., 2020).
While CFM is called “monitoring”, this is actually a misnomer. All these devices record information, they don’t actually monitor anything. Monitoring requires that an actual person interrogates the information produced by the recording in an informed manner, and that they are able to take action on what they see in order to made a difference. I am yet to see an answer to the question: who will be watching the CFM recordings? If they are only viewed in retrospect, then they are likely to be of little value. Will the data be projected to the central monitoring station in birth suite, so that clinicians who are already busy juggling responsibility for women in labour also need to attend to women who are at home? Will we create a new breed of maternity clinician whose sole role will be to sit and watch CFM outputs for a number of women for an entire shift? How will the person viewing the recording be able to take action? Are they meant to ring the woman who is sleeping at home and tell her to change position, and if that doesn’t help to summon an ambulance? And what of the psychological trauma that might be experienced by someone who has to rouse the woman, summon assistance, or transport her to care, all while watching her fetus deteriorate in real time on the monitor screen?
I’m concerned about what the experience of CFM will be like for women. Patriarchal values consider that woman’s primary social function (along with providing pleasure and ease for men and others) is to produce offspring. Feminists have for a very long time challenged the notion that women are simply a vessel for incubating the fetus and the social consequences that flow from that. Will wearing CFM reinforce the idea that the fetus should be the woman’s one and only concern during every moment of the day and night, and that her full participation in the world is a threat to her function in society? Requiring women to lie still for the duration of a standard antenatal CTG is achievable. Asking them to reduce movements over a full day, or longer, is not realistic. Neither is the expectation that at any moment they might be contacted by someone who has seen the monitor output and expected to attend the hospital, possibly immediately.
It remains possible that I may be wrong about CFM and that it might turn out to be THE thing that produces the long hoped-for sustained drop in perinatal mortality and that it protects the fetal brain and other organs from damage. However, it seems to me that CFM is an attempt to up the dose of an ineffective treatment, in the hope that more of the same thing will actually work. The best evidence we have about antenatal CTG monitoring (which is poor evidence to start with) is that it possibly increases perinatal mortality, so imagining why anyone might think that CFM will work is beyond me at present. Given the history of the introduction and expansion of all forms of CTG monitoring technology, I have grave concerns that we will once again find ourselves having to work around a technology without clear evidence that it actually works, simply because many people believe that it might work, if we just tried a bit harder. It is absolutely vital that appropriately powered, well designed research is conducted before CFM systems are introduced into clinical practice, and that they demonstrate clear benefits for the baby, in a way that is acceptable to women, and cost effective for society.
Bellussi, F., Po, G., Livi, A., Saccone, G., De Vivo, V., Oliver, E. A., & Berghella, V. (2020). Fetal movement counting and perinatal mortality: A systematic review and meta-analysis. Obstetrics and Gynecology. https://doi.org/10.1097/AOG.0000000000003645
Cahill, A. G., Tuuli, M. G., Stout, M. J., López, J. D., & Macones, G. A. (2018). A prospective cohort study of fetal heart rate monitoring: deceleration area is predictive of fetal acidemia. American Journal of Obstetrics and Gynecology, 218(5), 523.e521-523.e512. https://doi.org/10.1016/j.ajog.2018.01.026
Tamber, K. K., Hayes, D. J. L., Carey, S. J., Wijekoon, J. H. B., & Heazell, A. E. P. (2020). A systematic scoping review to identify the design and assess the performance of devices for antenatal continuous fetal monitoring. PLoS ONE, 15(12), e0242983. https://doi.org/10.1371/journal.pone.0242983