Admission CTGs: Do they improve outcomes?

An admission CTG is a relatively short period of CTG monitoring, typically 20 – 30 minutes long, performed when a woman first presents in labour to a hospital or birth centre. The theory behind admission CTGs is that when used for women without a risk factor that would lead to a recommendation for continuous CTG monitoring during labour, they identify women who might be at risk for experiencing a poor perinatal outcome. CTG monitoring would then be recommended for the rest of their labour. This assumes that using CTG monitoring during labour improve outcomes – which you may recognise as an early, and major flaw in this argument.

What does the Cochrane review say?

Evidence from randomised controlled trials comparing the use of admission CTG monitoring with intermittent auscultation in women considered to be at low risk at the time of presentation to hospital was most recently summarised in a Cochrane review by Devane et al. in 2017. They found four trials, conducted between 2001 and 2008, including 13,269 women. The authors of the Cochrane review found no statistically significant differences in:

Perinatal death (stillbirth + neonatal death). This occurred at a rate of one death per 1000 births in both groups.
Low Apgar scores (< 7) at 5 minutes of age. This occurred at a rate of 7 per 1000 births in both groups.
Admission to the nursery. This occurred at a rate of 39 per 1000 in the CTG group and 38 per 1000 in the intermittent auscultation group.
Hypoxic ischaemic encephalopathy (early signs that brain injury due to low oxygen may have happened). This occurred at a rate of 5 per 1000 in the CTG group and 4 per 1000 in the intermittent auscultation group.
Neonatal seizures. This occurred at a rate of 2 per 1000 in the CTG group and 3 per 1000 in the intermittent auscultation group.

In summary, the use of admission CTG monitoring didn’t improve outcomes for the baby.

Fortunately, each these outcomes is rare. But that means you need a really big sample size to know for sure whether there really is a difference or not. You can argue the result here is more a case of there being an absence of evidence of effectiveness, than of evidence of an absence of effectiveness. The rate of use of continuous CTG monitoring for the rest of labour was significantly higher among women who had an admission CTG performed (56% of women compared to 42% of women who did not, a 30% increase), so the failure to improve outcomes was not because CTG monitoring was not used.

What about the women?

What about the potential for harm for women from the use of admission CTGs? There were statistically significant increases in:

Caesarean section, rising from 3.6 per 100 to 4.4 per 100 when admission CTG was used, an increase of 20% (yes these rates are low! They serve as a reminder that in our recent past the caesarean section rate was lower, yet with a similar perinatal mortality rate).
Instrumental birth, rising from 12.6 per 100 to 13.8 per 100 when admission CTG was used, an increase of 10%.

Despite the lack of evidence in favour of admission CTG use, their use continues to be widespread in some places and not so much in others.

An evidence update

2008, when the last trial was done, was a long time ago. Katy Perry was singing about kissing a girl and liking it, and Slumdog Millionaire was doing serious numbers in cinemas (at least in my part of the world). One more trial has been done since the 2017 Cochrane review (Smith et al., 2018, the ADCAR trial). The planned size was based on the number of women needing to be enrolled to demonstrate a difference in the caesarean section rate. The researchers weren’t able to recruit enough women to meet this target, so it too remained underpowered to detect a difference in either the caesarean section rate, or in perinatal morbidity and mortality.

3034 women participated in the trial, and there were no deaths in either group. The rates of ongoing CTG use for labour were high in both groups at 72% (intermittent auscultation on admission) and 86% (admission CTG). There were no differences in the incidence of low Apgars scores at five minutes of age, cord blood acidosis, or admission to the nursery. There were also no differences in the caesarean section rate (6.9% in the CTG group and 8.6% in the intermittent auscultation group), or in the instrumental birth rate (20% in both groups).

What does this mean?

What you decide to do with this information really depends on the philosophical position you take about technology use in maternity care. The position taken by many is that admission CTG monitoring should continue to be used until we can clearly prove beyond all doubt that they really don’t work. This is combined with an acceptance that the associated increase in surgical birth is an acceptable price to pay.

I struggle with that position. I consider it unethical to continue to offer a technology that was introduced into practice without adequate evaluation, for which we have no evidence of benefit, and some evidence of harm. In what other branch of healthcare would this be considered appropriate?

It is my experience that birthing women are given incomplete and inaccurate information about admission CTG monitoring. The discussion is typically along the lines of “I’m just going to pop a trace on for a little while to see if your baby is happy” – which is quite inadequate to support informed decision making. Let’s start having honest discussions with birthing women about admission CTGs, support their decision-making processes, and honour the decisions they make.

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References

Devane, D., Lalor, J., Daly, S., McGuire, W., Cuthbert, A., Smith, V. (2017). Cardiotocography versus intermittent auscultation of fetal heart on admission to labour ward for assessment of fetal wellbeing. Cochrane Database of Systematic Reviews, 1(3), CD005122. https://dx.doi.org/10.1002/14651858.cd005122.pub5

Smith, V., Begley, C., Newell, J., Higgins, S., Murphy, D., White, M., Morrison, J., Canny, S., O’Donovan, D., Devane, D. (2018). Admission cardiotocography versus intermittent auscultation of the fetal heart in low‐risk pregnancy during evaluation for possible labour admission – a multicentre randomised trial: the ADCAR trial. BJOG: An International Journal of Obstetrics & Gynaecology, 126(1), 114-121. https://dx.doi.org/10.1111/1471-0528.15448