NIHR Signal A new method for monitoring baby’s heart beat during labour probably not justified

Published on 1 March 2016

A new way of monitoring a baby’s distress during labour, called ST waveform analysis, did not improve outcomes for the baby or reduce the likelihood of a caesarean section compared to current practice. Although monitoring of babies’ heartbeats during labour is common practice in the UK, additional ST analysis is not commonly used and on the basis of this evidence probably should not be promoted for routine use yet.

The outcomes measured in this review included death of the baby before or after birth, fits and brain damage from low oxygen levels. Finding babies at risk of these rare events is important as urgent delivery may save the baby. However if there is a role for ST analysis in this, it is not yet clear and larger trials would be needed.

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Why was this study needed?

Cardiotocography is a technology that can be used to monitor a baby’s heartbeat before or during birth. Certain patterns of changes in the baby's heartbeat may signal low oxygen levels in the baby meaning that expediting delivery by caesarean section or assisted delivery using forceps may be required.

However, cardiotocography is often criticised for having a high false-positive rate, resulting in unnecessary interventions such as caesarean birth. To reduce the number of false positives the use of ST analysis alongside cardiotocography has been proposed. ST analysis uses electrocardiogram changes – a measure of the heart’s electrical activity – to detect if the baby’s heart is suitably compensating to low oxygen levels implied by the heart rate changes detected by the cardiotocograph. This is thought to improve the diagnostic accuracy of the cardiotocograph, arguably leading to better outcomes for the baby (neonatal outcomes) and avoiding unnecessary interventions.

This aim of this review was to see if adding ST analysis to cardiotocography improved neonatal outcomes and reduced the number of caesareans.

What did this study do?

This was a systematic review and meta-analysis of six randomised controlled trials that compared foetal monitoring during 26,529 labours and deliveries using cardiotocography plus ST analysis versus cardiotocography alone. Deliveries were all at term or near term with the baby in the usual head down position (cephalic presentation). All trials included training for practitioners using ST analysis. The trials were in England, Sweden, Finland, France, The Netherlands and the USA. The American trial was the largest, randomising 11,108 patients – nearly half of the total number of patients included in the review.

The main outcome was a composite measure, a combination of neonatal outcomes including: the child’s death or suffering of seizures during birth or up to 28 days after birth, the need for emergency treatment after birth (measured either as a five minute Apgar score of three or less, or the need for mechanical ventilation) or foetal metabolic acidosis (high acid blood levels, suggestive of oxygen deficiency).

This was a high quality review with a low risk of bias in the included trials.

What did it find?

  • There was no difference in the composite outcome between groups – 1.5% in the cardiotocography and ST analysis group compared with 1.6% in the cardiotocography alone group (relative risk [RR] 0.90, 95% confidence interval [CI] 0.74 to 1.10; from a meta-analysis of five trials).
  • There were no statistically significant differences found between groups for any of the outcomes when considered individually.
  • No differences were seen between groups in the incidence of caesarean delivery – 13.8% in the cardiotocography and ST analysis group compared with 14% in the cardiotocography alone group (RR 0.96, 95% CI 0.85 to 1.08; six trials).

What does current guidance say on this issue?

The 2014 NICE guideline on intrapartum care recommends that cardiotocography is only used for women with certain risk factors, such as foetal heart rate abnormalities. It states that when in use, practitioners must ensure that the focus of care remains on the woman rather than the cardiotocograph trace, and that care decisions are not made on the basis of cardiotocography findings alone.

The guideline makes no recommendation with regard to the use of ST analysis.

What are the implications?

Because of the rarity of the outcomes being measured, very large trials would be needed to show a difference between these technologies, if one existed. This review remains too small to be the final word on the use of ST analysis.

However, for now the review confirms that adding ST analysis to cardiotocography did not decrease the chance of caesarean delivery, a more frequent occurrence. As ST analysis is not currently usual practice in the NHS, the evidence-base does not support investment in the technology.

Citation and Funding

Saccone G, Schuit E, Amer-Wåhlin I, et al. Electrocardiogram ST Analysis During Labor: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Obstet Gynecol. 2016;127(1):127-35.

No funding information was provided for this study.

Bibliography

Medline Plus. Apgar score.  Bethesda (MD): U.S. National Library of Medicine; 2014.

NICE. Intrapartum care quality standard. QS105. London: National Institute for Health and Care Excellence; 2015.

NICE. Intrapartum care for healthy women and babies. CG190. London: National Institute for Health and Care Excellence; 2014.

Patient UK. Intrapartum Fetal Monitoring – professional reference. Leeds: EMIS Group; 2015.

Why was this study needed?

Cardiotocography is a technology that can be used to monitor a baby’s heartbeat before or during birth. Certain patterns of changes in the baby's heartbeat may signal low oxygen levels in the baby meaning that expediting delivery by caesarean section or assisted delivery using forceps may be required.

However, cardiotocography is often criticised for having a high false-positive rate, resulting in unnecessary interventions such as caesarean birth. To reduce the number of false positives the use of ST analysis alongside cardiotocography has been proposed. ST analysis uses electrocardiogram changes – a measure of the heart’s electrical activity – to detect if the baby’s heart is suitably compensating to low oxygen levels implied by the heart rate changes detected by the cardiotocograph. This is thought to improve the diagnostic accuracy of the cardiotocograph, arguably leading to better outcomes for the baby (neonatal outcomes) and avoiding unnecessary interventions.

This aim of this review was to see if adding ST analysis to cardiotocography improved neonatal outcomes and reduced the number of caesareans.

What did this study do?

This was a systematic review and meta-analysis of six randomised controlled trials that compared foetal monitoring during 26,529 labours and deliveries using cardiotocography plus ST analysis versus cardiotocography alone. Deliveries were all at term or near term with the baby in the usual head down position (cephalic presentation). All trials included training for practitioners using ST analysis. The trials were in England, Sweden, Finland, France, The Netherlands and the USA. The American trial was the largest, randomising 11,108 patients – nearly half of the total number of patients included in the review.

The main outcome was a composite measure, a combination of neonatal outcomes including: the child’s death or suffering of seizures during birth or up to 28 days after birth, the need for emergency treatment after birth (measured either as a five minute Apgar score of three or less, or the need for mechanical ventilation) or foetal metabolic acidosis (high acid blood levels, suggestive of oxygen deficiency).

This was a high quality review with a low risk of bias in the included trials.

What did it find?

  • There was no difference in the composite outcome between groups – 1.5% in the cardiotocography and ST analysis group compared with 1.6% in the cardiotocography alone group (relative risk [RR] 0.90, 95% confidence interval [CI] 0.74 to 1.10; from a meta-analysis of five trials).
  • There were no statistically significant differences found between groups for any of the outcomes when considered individually.
  • No differences were seen between groups in the incidence of caesarean delivery – 13.8% in the cardiotocography and ST analysis group compared with 14% in the cardiotocography alone group (RR 0.96, 95% CI 0.85 to 1.08; six trials).

What does current guidance say on this issue?

The 2014 NICE guideline on intrapartum care recommends that cardiotocography is only used for women with certain risk factors, such as foetal heart rate abnormalities. It states that when in use, practitioners must ensure that the focus of care remains on the woman rather than the cardiotocograph trace, and that care decisions are not made on the basis of cardiotocography findings alone.

The guideline makes no recommendation with regard to the use of ST analysis.

What are the implications?

Because of the rarity of the outcomes being measured, very large trials would be needed to show a difference between these technologies, if one existed. This review remains too small to be the final word on the use of ST analysis.

However, for now the review confirms that adding ST analysis to cardiotocography did not decrease the chance of caesarean delivery, a more frequent occurrence. As ST analysis is not currently usual practice in the NHS, the evidence-base does not support investment in the technology.

Citation and Funding

Saccone G, Schuit E, Amer-Wåhlin I, et al. Electrocardiogram ST Analysis During Labor: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Obstet Gynecol. 2016;127(1):127-35.

No funding information was provided for this study.

Bibliography

Medline Plus. Apgar score.  Bethesda (MD): U.S. National Library of Medicine; 2014.

NICE. Intrapartum care quality standard. QS105. London: National Institute for Health and Care Excellence; 2015.

NICE. Intrapartum care for healthy women and babies. CG190. London: National Institute for Health and Care Excellence; 2014.

Patient UK. Intrapartum Fetal Monitoring – professional reference. Leeds: EMIS Group; 2015.

Electrocardiogram ST Analysis During Labor: A Systematic Review and Meta-analysis of Randomized Controlled Trials

Published on 10 December 2015

Saccone, G.,Schuit, E.,Amer-Wahlin, I.,Xodo, S.,Berghella, V.

Obstet Gynecol , 2015

OBJECTIVE: To compare the effectiveness of cardiotocography plus ST analysis with cardiotocography alone during labor. DATA SOURCES: Randomized controlled trials were identified by searching electronic databases. METHODS OF STUDY SELECTION: We included all randomized controlled trials comparing intrapartum fetal monitoring with cardiotocography plus ST analysis with cardiotocography alone. The primary outcome (ie, perinatal composite outcome) was a composite of intrapartum fetal death, neonatal death, Apgar score 3 or less at 5 minutes, neonatal seizure, metabolic acidosis (defined as umbilical arterial pH 7.05 or less, and extracellular fluid base deficit 12 mmol/L or greater), intubation for ventilation at delivery, or neonatal encephalopathy. TABULATION, INTEGRATION, AND RESULTS: Six randomized controlled trials, which included 26,529 laboring singletons with cephalic presentation at term, were analyzed. Compared with women who were randomized to cardiotocography, those who were randomized to ST analysis and cardiotocography had a similar incidence of perinatal composite outcome (1.5% compared with 1.6%; relative risk [RR] 0.90, 95% confidence interval [CI] 0.74-1.10; five studies), neonatal metabolic acidosis (0.5% compared with 0.7%; RR 0.74, 95% CI 0.54-1.02; five studies), admission to the neonatal intensive care unit (5.4% compared with 5.5%; RR 0.99, 95% CI 0.90-1.10; six studies), perinatal death (0.1% compared with 0.1%; RR 1.71, 95% CI 0.67-4.33; six studies), neonatal encephalopathy (0.1% compared with 0.2%; RR 0.62, 95% CI 0.25-1.52; six studies), cesarean delivery (13.8% compared with 14.0%; RR 0.96, 95% CI 0.85-1.08; six studies), and operative delivery (either cesarean or operative vaginal delivery) (23.9% compared with 25.1%; RR 0.93, 95% CI 0.86-1.01; six studies). CONCLUSION: The use of ST analysis during labor as an adjunct to the standard cardiotocography does not improve perinatal outcomes or decrease cesarean delivery.

Foetal monitoring in labour is done to detect changes in a baby’s heart rate which could be a sign the baby is distressed and low on oxygen meaning that something such as a caesarean section needs to be done quickly to deliver the baby. There are different ways of monitoring the baby’s heartbeat in labour:

  • Intermittently monitoring is when a midwife listens, at least one minute every 15 minutes through established labour, using a handheld ultrasound monitor. This method does not restrict movement.
  • A machine called a CTG (cardiotocograph) monitors the heart beat continuously and a small monitor is strapped to the mother’s tummy on a belt. How far the mother can move will depend on the type of machine.
  • A scalp clip is sometimes used if the midwife cannot get a good trace of the baby's heart rate through the abdomen. This is put on during a vaginal examination and the waters will be broken if they have not already done so.
  • The ST analysis machine consists of a monitor showing the baby’s CTG and analysis of an electrocardiograph (ECG) continuously. It is attached to the baby by a scalp clip. The clip records the total ECG signal necessary for ST analysis and CTG at the same time. When the monitor detects any significant change in the ST interval, these are displayed as "ST events" on the main screen.

The Apgar score, developed in 1952 by Virginia Apgar, is designed to quickly assess a new-born’s physical condition and whether medical or emergency attention may be required. Five factors are evaluated: skin colour, pulse, reflexes, muscle tone and breathing rate or effort. Each is scored on a scale of 0 to 2, giving a total score of 0 to 10. The higher the score, the better the baby is doing after birth. Any score lower than seven is a sign that the baby needs medical attention. The lower the score, the more help the baby needs.

Expert commentary

This study illustrates the fundamental challenges of evaluating health interventions when the outcomes of interest are rare. The authors conclude from their review that there is no benefit of using ST analysis over and above standard cardiotocography. However, this conclusion is not entirely correct, and neither is their statement that these were “appropriately powered” trials. The really substantive outcome of interest with this intervention is perinatal mortality with an incidence of 1 per 1000 births. To detect a 25% relative risk reduction to 0.75 per 1000 (which is a large effect considering that women are already having cardiotocography), then the required sample size is around 600,000 women (compared with 26,000 in this meta-analysis). It would therefore be correct to say that there is, as yet, no evidence that ST analysis improves neonatal outcome, but this is not the same as saying that ST analysis offers no benefits. The existing trials, even when added together, are simply too small to be certain that this technology does not save lives.

Professor Peter Brocklehurst, Director of the Institute of Women's Health and Professor of Women's Health, University College London