An admission CTG is a relatively short period of CTG monitoring, typically 20 – 30 minutes long, performed when a woman first presents to a hospital or birth centre in labour. The theory behind the use of admission CTGs is that when used for women who are considered to not have an indication for continuous intrapartum CTG monitoring, they identify women who might be at risk for experiencing a poor perinatal outcome, and for whom CTG monitoring would then be recommended. This assumes that using intrapartum CTG monitoring will then improve outcomes – which is something I’ll tackle in a later post.
The outcomes that CTG monitoring is designed to address are those considered to occur secondary to low oxygen levels (hypoxia): namely intrapartum stillbirth, neonatal death, or encephalopathy (brain injury) which might potentially lead to cerebral palsy. Because these are uncommon, “surrogate” measures are often used in research instead – that is more common outcomes which are considered to occur more commonly when the fetus experiences hypoxia.
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, which included 13,269 women. The authors of the Cochrane review found no statistically significant differences in the following outcomes:
- Perinatal death (stillbirth + neonatal death). This occurred at a rate of one death per 1100 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 encephalopathy. 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 has not been shown to improve perinatal outcomes.
The sample size was relatively small given the low incidence of the outcomes of interest, so it 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 intrapartum CTG monitoring 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 intrapartum CTG monitoring was not used.
What about the potential for harm from the use of admission CTGs? There were statistically significant increases in:
- Caesarean section, rising from 36 per 1000 to 44 per 1000 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 very similar perinatal mortality rate).
- Instrumental birth, rising from 126 per 1000 to 138 per 1000 when admission CTG was used, an increase of 10%.
Despite the relative lack of evidence of benefit of an approach that continues to be widespread in practice, little research attention in the past decade has focussed on undertaking sufficiently large trials to resolve any remaining uncertainty. One recent trial has been undertaken (Smith et al., 2018, the ADCAR trial) but the planned size was based on the number of women needing to be enrolled to demonstrate a difference in the caesarean section rate, and even this was not achieved, 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 perinatal deaths in either group. The rates of continuous intrapartum CTG use 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 you decide to do with this information really depends on the philosophical position you take with respect to the use of technology in maternity care. The position taken by many is that admission CTG monitoring should continue to be used until such time that we have sufficient evidence to 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 personally struggle with that position. Is it ethical to continue to offer a technology which was introduced into practice without adequate evaluation, for which we have no evidence of benefit, but 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.
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