9 Current Scientific Evidence on CTG. Handbook CTG

 9

Current Scientific Evidence on CTG

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Ana Piñas Carrillo and Edwin Chandraharan

Handbook of CTG Interpretation: From Patterns to Physiology, ed. Edwin Chandraharan.

Published by Cambridge University Press. © Cambridge University Press 2017.

Key Facts

Current Evidence

CTG has been used since the 1960s. It was introduced as a method of

intrapartum fetal monitoring in high-risk pregnancies to improve neonatal

outcomes and to avoid long-term neurological sequelae. However, the rates of

perinatal deaths, hypoxic encephalopathy and cerebral palsy have remained

stable, whereas the rate of operative deliveries among fetuses monitored using

CTG has been continuously increasing.

CTG interpretation, which has been based on pattern recognition, has a poor

positive predictive value for intrapartum hypoxia and a high false-positive rate.

Only about 40–60 per cent fetuses with a CTG classified as abnormal by NICE

guidelines have evidence of metabolic acidosis at birth.

The latest Cochrane Review, published in 2013, included 13 trials (>37,000

women). However, only two of these trials were considered of high quality.Interpretation of Current Evidence

The use of continuous intrapartum CTG monitoring showed no significant

difference in overall perinatal mortality rate. It showed a 50 per cent reduction

in neonatal seizures; however, this did not translate to any long-term benefit such

as a significant reduction in cerebral palsy.

Continuous CTG monitoring showed a significant increase in operative

deliveries, both caesarean sections and instrumental deliveries.

The use of additional tests such as fetal blood sampling did not change the longterm outcomes but increased the rate of operative deliveries.

Some individual studies (e.g. Vintzelios et al.) have suggested that the use of

CTG may help improve perinatal outcomes.

To measure rare outcomes such as perinatal deaths and cerebral palsy (incidence

2/1,000), large number of babies need to be recruited to reach scientific

conclusions.

It is estimated that 80,000 women need to be enrolled in a study to achieve the

‘power of the rest’ to reach conclusions with regard to the reduction in cerebral

palsy and perinatal deaths. So far, Cochrane Review has analysed only 37,000

women, and only two of the trials were of high quality.

Earlier clinical trials on CTG and intermittent auscultation were heterogeneous

with different cut-off values to determine neonatal outcomes and different

criteria for ‘pathological’ CTG traces.

There has been a continuous improvement in both obstetric and neonatal care

since the CTG was introduced into clinical practice. Therefore, the older trials,

which showed no evidence of benefit, may not be applicable in current obstetric

practice.

There were over 25 different clinical guidelines, each employing different

classification systems and indications for continuous, electronic fetal heart rateFuture Developments

(FHR) monitoring until the mid-1980s. Therefore, the older clinical trials did

not use standardized criteria for continuous, electronic FHR monitoring.

The largest randomized controlled trial, ‘The Dublin Trial’, that compared

intermittent auscultation versus continuous, electronic FHR monitoring used fetal

scalp blood sampling on both arms, which is not an accepted clinical practice. In

addition, artificial rupture of membranes was performed at 1 cm dilatation of the

cervix to exclude meconium staining of liquor in the ‘intermittent monitoring

group’, which is also not an accepted clinical practice. Therefore, the findings of

the Cochrane Review, which have been skewed by this largest randomized trial

on intermittent auscultation versus CTG, should be used with caution in 2015.

It is also very important to appreciate that earlier studies purely used ‘pattern

recognition’ to classify CTGs without considering fetal physiological response

to hypoxic stress. It has been well known that ‘pattern recognition’ is associated

with significant inter- and intra-observer variability. Therefore, the reported

increase in operative interventions may be secondary to overreaction to

observed patterns. Conversely, a lack of understanding of pathophysiology of

CTG and features of fetal decompensation may have resulted in poor perinatal

outcomes.

Therefore, it is hoped that the use of fetal physiology while interpreting CTG

traces and timely and appropriate action when features of fetal decompensation

are observed on the CTG while using intrauterine resuscitation to improve fetal

intrauterine environment may help improve perinatal outcomes while reducing

unnecessary operative interventions.

There are two large multicentre randomized controlled trials (‘INFANT’ trial

and ‘CisPorto’ trial) on electronic FHR monitoring which have been recently

completed and the results are awaited. It is hoped that these will further increase

the number of ‘high-quality’ evidence to appropriate conclusion with regard toFurther Reading

1. Alfirevic Z, Devane D, Gyte GML. Continuous cardiotocography (CTG) as a form of

electronic fetal monitoring (EFM) for fetal assessment during labor. Cochrane Database Syst

Rev. 2013; 5: CD006066.

2. Chen HY, Chauhan S, Ananth C, Vintzileos A, Abuhamad A. Electronic fetal heart rate

monitoring and its relationship to neonatal and infant mortality in the United States. Am J

Obstet Gynecol. 2011; 204: e1–10.

3. Donker D, van Geijn H, Hasman A. Interobserver variation in the assessment of fetal heart

rate recordings. Eur J Obstet Gynecol Reprod Biol. 1993; 52: 21–28.

4. Macdonald D, Grant A, Sheridan-Pereira M, Boylan P, Chalmers I. The Dublin

randomized controlled trial of intrapartum fetal heart rate monitoring. Am J Obstet Gynecol.

1985; 152: 524–39.

5. Khangura T, Chandraharan, E. Electronic fetal heart rate monitoring: the future. Curr

Women’s Health Rev. 2013; 9: 169–74.