Birth Small Talk

Talking about birth

Mysterious cats and CTG monitoring

Kahlua aka #PhDCat

Early last year I wrote a post about Dr Who and alternative universes, highlighting the way that people make meaning of their individual experiences. For those of us who are health practitioners, it is important to reflect on the way we make meaning because it is easy to slip into what are known as cognitive biases. We can’t always avoid these, but it does help to have examples of such biases to increase the chance that we will catch them before we act on them in ways that are not helpful.

Back in January, Alencar Neto, Farina, and Nunes Sampaio (2021) proposed a new cognitive bias, and I think it helps make sense of our propensity to use CTG monitoring. You can read the full paper here. They named their bias for Schrödinger’s Cat. If you aren’t familiar with the term, it relates to a concept from quantum mechanics. An unseen cat can be considered simultaneously to be both alive AND dead in the absence of additional information about the actual state of the cat. 

The authors provide examples of several possible different timelines (a bit like my Dr Who suggestion) that reinforce beliefs that ineffective therapies work. 

I think the Schrödinger’s Cat cognitive bias works for CTG monitoring as well. Using the data from Analysis 1.1 (Alfirevic et al., 2017) 3 in 1000 babies die around the time of birth, and this is the same whether CTG monitoring or intermittent auscultation is used. Let’s look at some possible timelines and see how the Schrödinger’s Cat bias might play out.

Timeline 1.1. A woman has CTG monitoring and her baby is born alive. Both she and her care providers belief that CTG monitoring is effective is reinforced.

Timeline 1.2. A woman has CTG monitoring and her baby dies. One common way that people make sense of this is to blame one or more clinicians for not having correctly interpreted the CTG. The belief that CTG monitoring is effective in preventing perinatal death is reinforced. 

Timeline 2.1. A woman has intermittent auscultation, and her baby is born alive. She is considered to have been lucky to have got away with such a risky decision. The belief that CTG monitoring is effective remains unchallenged.

Timeline 2.2. A woman has intermittent auscultation, and her baby dies. This is considered as prima facie evidence of unprofessional practice, and the belief that CTG monitoring would have prevented this from happening is reinforced.

As you can see, in the moment that the decision to use, or not, CTG monitoring is made, two possible futures exist simultaneously – the survival of the baby or its death (fortunately rare). Research evidence has shown that each of these two possible futures are just as likely to occur regardless of which fetal monitoring method is chosen. At the time of decision making this evidence is set aside in favour of the Schrödinger’s Cat bias which assumes the best outcome is more likely to occur if CTG monitoring is used, and the worst outcome is more likely if intermittent auscultation is used.  

Cognitive biases are tricky. It is very difficult to spot when you are in the midst of one, particularly when the bias is one that is held to be true by the culture in which we operate. Generating and using sound research findings are the only way that we can open the box and see whether the cat is actually alive or dead. 


Alencar Neto, J., Farina, E., Nunes Sampaio, M. (2021, Jan). Schrödinger’s Cat Bias: A New Cognitive Bias Proposed. Cureus 13(1), e12697.

Alfirevic, Z., Devane, D., Gyte, G. M. L., & Cuthbert, A. (2017, Feb 03). Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour. Cochrane Database of Systematic Reviews, 2(CD006066), 1-137.

Categories: CTG, EFM, IA, Philosophy

Tags: , , ,

2 replies

  1. A fascinating article Kirsten and along your perspective on the matter. Regrettably because CTGs are concreted into the institutional and medico legal reviews , it is hard to have any rational discussion on the matter, The other problem is that the research itself is often problematic because of the lack of blinding and the preexisiting biases in which context the research is done , along with this is the vested interests ( e.g Infant study).



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