Loud CTGs – turn it off! – Birth Small Talk

Sometimes I spot a new research paper and I ended up thinking – well that was something I never really thought about before! That was what happened when this one came my way. I’m pleased someone thought to do this research and I hope maternity professionals can adopt their practice with these findings in mind.

How was it done?

The paper has the slightly confusing title of “The effect of nonstress device noise level on stress parameters in primigravida women: A randomised controlled trial” (Aysenur et al, 2024). Nonstress testing (or NST) is another name for antenatal CTG use. The term non stress test is used to distinguish it from the now rarely used stress test, where contractions were deliberately provoked to see how the fetal heart rate would respond – testing whether the fetus would be “stressed”. Women pregnant for the first time (primigravida), in the third trimester of their pregnancy, with one fetus, who had been recommended to have an antenatal CTG were enrolled in this trial, conducted in Turkey.

The authors were interested in finding out whether the noise typically generated by a CTG machine increased stress in the women being tested. Once women agreed to be involved in the study, they were randomly divided into four groups. One had the sound of the CTG turned off completely, and the three other groups had the sound on but set at one of three different levels (1 – 35 dB, 36 – 60 dB, or more than 60 dB). To find out who had more stress, blood pressure, heart rate, oxygen saturation, blood glucose, and salivary cortisol and adrenocorticotrophic hormone levels were measured before the CTG was started, half way through the test, and two minutes after it was finished. Women’s self-reports of their level of stress were not sought (this is a pity – is this because researchers don’t believe women unless they have another way to scientifically prove what women say?).

What did they find?

44 women took part in the research. We aren’t told why they were having the antenatal CTG testing done. They were divided equally between the four groups. No differences in blood pressure or oxygen saturation levels were found between the four groups. Women’s heart rates did go up over time, with larger rises as the noise volume increased. Blood glucose and cortisol levels also rose over time with increased noise volume, with no differences in adrenocorticotrophic hormone levels.

What does this mean?

This research provides evidence of a physiological stress response to the noise generated by antenatal CTG monitoring. I have written before about the relationship between women’s stress levels and fetal heart rate patterns (here). Avoiding increased stress levels isn’t simply a nice soft touch, it potentially also has health consequences for the woman and her baby.

Maternity professionals read visual information on the CTG to determine whether the heart rate pattern is normal or not. It can be handy to have the volume up when CTG monitoring is used during labour – when decelerations are more common. In labour, the maternity professional is more likely to be distracted by other tasks and might choose to make use the background sound of the fetal heart beat as a clue they need to look at the CTG recording. But this isn’t true for antenatal CTG monitoring where the period of monitoring is brief (typically 20 minutes). I can’t see any good reason why, if a woman chooses antenatal CTG monitoring, the sound should be turned on.

While this study was small and is far from being definitive proof of harm – it suggests there might be a problem with the noisy CTG. If you are the woman having one – ask for the sound to be turned off. If you are the professional performing the CTG, turn the volume off unless the woman specifically requests it to be on, and then make the volume as low as possible to meet her needs.

[If your service is so short-staffed that you rely on having the volume really loud so you can hear it from the next room – have a big long think about whether you should tolerate working in a service that can’t provide safe care and attempts to make it look safe at the expense of women’s experiences of their care and their health outcomes.]

Before I sign off, I’d also like to remind you that evidence about antenatal CTG does NOT show it improves outcomes for the fetus / baby, and might in fact make things worse. You can read more about the evidence base here.

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References

Aysenur, T., Nuran, G., Cihan, K., & Huri, B. (2024, Jan 4). The effect of nonstress device noise level on stress parameters in primigravid women: A randomized controlled trial. Journal of Midwifery & Women’s Health, in press. https://doi.org/10.1111/jmwh.13581 