Antenatal cardiotocography for fetal assessment (2024)

Monitoring Editor: Rosalie M Grivell, Zarko Alfirevic, Gillian ML Gyte, Declan Devane, and Cochrane Pregnancy and Childbirth Group

Flinders University and Flinders Medical Centre, Department of Obstetrics and Gynaecology, Bedford ParkSouth AustraliaAustralia, SA 5042

The University of Liverpool, Department of Women's and Children's Health, First Floor, Liverpool Women's NHS Foundation Trust, Crown Street, LiverpoolUK, L8 7SS

University of Liverpool, Cochrane Pregnancy and Childbirth Group, Department of Women's and Children's Health, First Floor, Liverpool Women's NHS Foundation Trust, Crown Street, LiverpoolUK, L8 7SS

National University of Ireland Galway, School of Nursing and Midwifery, University Road, GalwayIreland

Cardiotocography (a form of electronic fetal monitoring) for assessing a baby's well‐being in the womb during pregnancy

Some pregnancies can be complicated by a medical condition in the mother (e.g. diabetes or high blood pressure) or a condition that might affect the health or development of the baby. If these babies with potential difficulties could be identified, and if there were effective interventions to improve the outcomes, then an accurate test that could be used during pregnancy could be beneficial. Cardiotocography (CTG) is a continuous electronic record of the baby’s heart rate obtained via an ultrasound transducer placed on the mother’s abdomen. It is sometimes referred to as ‘electronic fetal monitoring’ (EFM). The review looked to see if using CTG during pregnancy might improve outcomes for babies by identifying those with complications.It looked for studies that included women at both increased risk, and at low risk, of complications. The review included six studies with all of the women at increased risk of complications.Four of the studies were undertaken in the 1980s and two in the late 1990s. The included studies were not of high quality. There were no differences in outcomes identified (low/very low quality evidence), although when computerised interpretation of the CTG trace was used, the findings looked promising.However, CTG monitors, associated technologies and the way midwives and obstetricians care for women with different complications in pregnancy have changed over the years. This means that more studies are needed now to see if outcomes for babies at increased risk of complications can be improved with antenatal CTG, particularly computerised CTG.

Description of the condition

Pregnancy may be complicated by conditions that need additional ways of assessment of fetal well‐being. These conditions include medical problems in the mother, which may impact on the fetus, pregnancy‐specific problems and diseases of the fetus in which fetal health may be affected. Medical problems in the mother that are associated with increased risk to the fetus include essential hypertension, pre‐eclampsia, renal and autoimmune disease, maternal diabetes and thyroid disease (Lloyd 2003a; LLoyd 2003b; Nelson‐Piercy 2001; NICE 2008b). Other situations in pregnancy that pose an increased risk to fetal health are prolonged pregnancy, vagin*l bleeding, reduced fetal movements and prolonged ruptured membranes (Gribbin 2006). Fetal conditions include intrauterine growth restriction and fetal infection; multiple pregnancies also increase the risks to the fetuses (Fisk 2001; Gribbin 2006). These risks include possible neurodevelopmental problems in infancy including non‐ambulant cerebral palsy, developmentaldelay, auditory and visual impairment. These can be quantified using validated tools such as Bayley Scales of Infant Development (Psychom*otor Developmental Index and Mental Developmental Index) (Bayley 1993).

The indication for additional fetal assessment in all of the above situations is a real, or perceived, increased risk of fetal compromise that might lead to morbidity or mortality in the fetus or newborn.

Description of the intervention

The cardiotocograph (CTG) is a continuous electronic record of the fetal heart rate obtained via an ultrasound transducer placed on the mother’s abdomen (external or indirect CTG). A second transducer is placed on the mother’s abdomen over the uterine fundus to record simultaneously the presence of any uterine activity. Both fetal heart rate and uterine activity are traced simultaneously onto a paper strip. Components of the fetal heart rate that can be assessed include: baseline rate, baseline variability, accelerations and decelerations. The relationship between fetal heart rate and the timing of uterine contractions is also assessed. Cardiotocography is used widely in maternity care, both in the antepartum and intrapartum periods. Although the theoretical basis for applying and interpreting the test and indications for monitoring are similar, the focus of this review is on the use of CTG during pregnancy and before labour starts. There is a separate Cochrane review on the effectiveness of continuous intrapartum cardiotocography (Alfirevic 2013).

The term 'electronic fetal monitoring' is sometimes used synonymously with CTG monitoring, but is considered to be a less precise term because (1) CTG monitoring also includes monitoring the mother's contractions and (2) other forms of fetal monitoring might also be classed as 'electronic', e.g. ECG, fetal pulse oximetry.

Antenatal CTG is a commonly used form of fetal assessment in pregnancy and uses the fetal heart rate as an indicator of fetal well‐being (Boyle 2004). It may be used in isolation, sometimes referred to as the ‘non‐stress test' or with the stimulation of uterine activity to see how the fetal heart responds, sometimes known as the ‘contraction stress test’ (Owen 2001).

Antenatal CTG is most commonly performed in the third trimester of pregnancy (after 28 weeks). The gestational age at which CTG commences varies in practice, and at least in part depends on the minimum age of survival in the local neonatal unit and therefore, in some institutions may be used even before 26 weeks' gestation (Smith 1987).

Antenatal CTG can also be used in combination with other methods of fetal assessment such as ultrasound Doppler measurements and amniotic fluid volume measurement (Turan 2008), and as part of a formal biophysical profile (where fetal movements, fetal tone and fetal breathing, and liquor volume are assessed, with or without assessment of the fetal heart rate) (Lalor 2008). Frequency of testing varies widely in practice, depending on the indication for the CTG and gestational age, and ranges from weekly to three times a day.

How the intervention might work

The underlying theoretical concept for the use of CTG in pregnancy is that it is a screening test for the identification of babies with acute or chronic fetal hypoxia or at risk of developing such hypoxia. Fetal hypoxia is believed to result in specific pathophysiological adaptations in the fetus, which in turn may cause changes in the pattern of the fetal heart rate parameters mentioned below (ACOG 1994). Therefore, accepted 'normal' limits for fetal heart rate parameters are used when interpreting antenatal CTGs.

The normal fetal heart rate varies with vagal and sympathetic tone adjustments and, therefore, varies with gestational age due to maturation of the fetal nervous system. Accepted normal parameters for the term fetus are reported as follows (Gribbin 2006; RCOG 2001).

1. Baseline fetal heart rate of 110 to 160 beats per minute.

2. Baseline variability should be greater than five beats per minute.

3. Presence of two or more accelerations of the fetal heart rate exceeding 15 beats per minute, sustained for at least 15 seconds in a 20‐minute period (Devoe 1990) ‐ this pattern is termed reactive.

4. Absence of decelerations.

In addition, consideration should be given to the frequency, duration, intensity and resting tone of uterine contractions and their relationship to the fetal heart rate pattern.

When the fetus is hypoxic, baseline heart rate variability and accelerations may decrease or disappear and decelerations in the fetal heart rate may occur (Gribbin 2006).

Why it is important to do this review

At present, CTG it is not recommended in the UK as a method of routine fetal assessment in low‐risk pregnancy (NICE 2008a). However, antenatal CTGs have been and continue to be used widely in the assessment of fetal well‐being during pregnancy in women at increased risk of complications.

Hence, it is important to systematically review the evidence on the effectiveness of antenatal CTG. This should be assessed in women at increased risk of complications that may adversely affect the fetus. If benefits are found for these women and babies, then it would be important to assess the potential benefits of using antenatal CTG assessments in all pregnancies. Other Cochrane reviews that relate to this topic include: 'Regimens of fetal surveillance for impaired fetal growth' (Grivell 2012a); 'Fetal and umbilical Doppler ultrasound in high‐risk pregnancies' (Alfirevic 2013a); 'Fetal and umbilical Doppler ultrasound in normal pregnancy' (Alfirevic 2015); 'Utero‐placental Doppler ultrasound in pregnancy' (Alfirevic 2010c); 'Biochemical tests for placental function' (Neilson 2012); 'Fetal movement counting for assessment of fetal well‐being' (Mangesi 2007); 'Fetal manipulation for facilitating tests of fetal well‐being' (Tan 2013); 'Fetal vibroacoustic stimulation for facilitating tests of fetal well‐being' (Tan 2013a); 'Maternal glucose administration for facilitating tests of fetal well‐being' (Tan 2012); 'Amniotic fluid index versus single deepest vertical pocket as a screening test for predicting adverse pregnancy outcomes' (Nabhan 2008); 'Biophysical profile for fetal assessment in high risk pregnancies' (Lalor 2008).

Criteria for considering studies for this review

Search methods for identification of studies

The following methods section of this review is based on a standard template used by the Cochrane Pregnancy and Childbirth Group.

Data collection and analysis

For methods used in the previous version of this review, seeGrivell 2012b.

Description of studies

SeeCharacteristics of included studies, Characteristics of excluded studies and Characteristics of studies awaiting classification.

Risk of bias in included studies

See Figure 1 for a summary of the 'Risk of bias' assessment.

We assessed included studies for methodological quality on the basis of selection bias (sequence generation and allocation concealment), performance bias (blinding), attrition bias (incomplete outcome data), and selective reporting bias (see 'Methods’ above). Overall, the studies were not of high quality, which was perhaps not surprising as four were undertaken in the 1980s and two in the 1990s when our understanding of the importance of the issues of risk of bias were not so well understood as they are now (Figure 1).

Effects of interventions

See: Table 1; Table 2

All the studies included in the review looked at women at increased risk of complications and none of the studies assessed women at low risk of complications. In addition, the lack of clarity regarding the quality of the studies, and the small numbers of studies included, meant that we were not always able to undertake sensitivity analyses by quality and the findings, therefore, remain uncertain.

Summary of main results

Antenatal cardiotocography (CTG) is a widely used method of fetal assessment and is commonly applied to a large and varied population of pregnant women and their babies. The basic technology that underlies the performance and application of the traditional CTG has changed little since its introduction more than 20 years ago. Despite concerns regarding the reliability and reproducibility of the antenatal CTG as a test of fetal assessment, it has widely infiltrated maternity care practice.

We have systematically reviewed the evidence on the effectiveness of antenatal CTG for the improvement of maternal and infant health. We have found no clear benefit for mothers or their babies in the studies included in this review.

Overall completeness and applicability of evidence

The included studies have limitations with regard to implications for current practice. Firstly, four of the six studies were undertaken in the 1980s during a time when both screening of and management of risks to fetal health were possibly different to current maternity care practice. For example, many of the included studies were undertaken at a time when practice included the use of many tests that are today considered obsolete (e.g. blood tests for placental function). Ultrasound assessment of fetal anatomy and, in particular, use of Doppler studies have improved in quality and become a useful tool for diagnosis and surveillance in pregnancies at high risk of complications (Alfirevic 2010a). Outcomes for premature babies have also improved greatly in terms of both survival and morbidity (Chan 2008). Some of these aspects may make the translation of results from studies performed in the 1980s difficult and less relevant to current practice. Secondly, all included studies were performed in high‐income countries. The use of a basic CTG might be feasible and affordable in certain healthcare settings where other tools to assess fetal health such as ultrasound might be unaffordable. Thirdly, despite the probable lack of high‐quality evidence to support this, fetal assessment in current practice often involves a combination of methods and this perhaps reduces the relevance of the effectiveness of a single method of testing. Fourthly, the review is clearly underpowered for assessing perinatal mortality.

Another limitation is that the included studies only recruited women at increased risk of complications. However, since these studies have failed to show a benefit for these women and their babies, then it is perhaps even less likely that a benefit would be found in low‐risk women.

One advantage of our review is a separate analysis of two small studies assessing the effects of computerised CTG. This type of CTG, with automated assessment of the heart rate parameters, may overcome some problems of standard CTG such as low reproducibility, inter‐ and intra‐observer variation in interpretation and high false positive rates. Further evaluation is, however, needed and should include consideration of women's and clinician's views. Pregnancies with complications may increase anxiety and women often value the 'human touch' when anxious in pregnancy. The evaluation of women's views with traditional CTG should also be a focus of further studies.

Quality of the evidence

The trials were not of high quality, which was perhaps not surprising as four were undertaken in the 1980s and two in the 1990s when our understanding of the importance of the issues of risk of bias were not so well understood as they are now. Gradepro software was used to assess the quality of evidence for the outcomes listed above under two comparisons 'traditional antenatal CTG versus no antenatal CTG and computerised antenatal CTG versus traditional antenatal CTG'. For the first comparison the quality of evidence was low for the outcome of perinatal mortality and caesarean section and very low for Apgar score below seven at five minutes. Other assigned outcomes were not reported by any of the included studies under this comparison. For the comparison of 'computerised antenatal CTG versus traditional antenatal CTG', the evidence was assessed as being moderate quality for the outcome of perinatal mortality, low for caesarean section and very low quality for Apgar score below seven at five minutes. Data were not available for the other three outcomes. Downgrading of evidence was based on including studies with unclear/high risk of bias and presence of imprecise results presented as wide confidence intervals crossing the line of no effect.

Potential biases in the review process

Our search strategy was supported by the Pregnancy and Childbirth Review Group. However we are aware that there is always the possibility of introducing bias to the review process. We have tried to minimise bias in a number of ways, including assigning two review authors to assess the appropriateness of inclusion or exclusion of studies, to carry out data extraction and to assess the risk of bias, and as such we have attempted to minimise biases in the review process.

Agreements and disagreements with other studies or reviews

Since the publication of the 2009 version of this review, there have been very few systematic reviews or meta‐analyses by other authors or groups. Many narrative reviews on the topic of fetal well‐being assessment have found no up‐to‐date information and conclusions have been based largely on this systematic review. A review by O'Neill and Thorp in 2012 (O'Neill 2012) reports, "there is no benefit from nonstress test (antenatal CTG) evaluation in isolation". This points to the issue that in current clinical practice, assessment of fetal health frequently involves a number of methods in combination. A number of other recent reviews also consider a range of assessment methods, and rarely comment upon the significance of CTG alone.

Implications for practice

We found no good evidence to support the use of traditional cardiotocography (CTG), or computerised CTG, in pregnancy for improving fetal outcomes. The data are not of high quality and lacked power to detect possible important differences in either benefit or harm. We recognise that many aspects of maternity care may have changed since the trials reviewed here were carried out, so new studies are needed to assess the effects of traditional and computerised antenatal CTG before they are used in clinical practice. In order to be relevant to current practice, future trials and reviews may need to assess not only antenatal CTG in isolation, but also combinations of different fetal assessment tests.

Implications for research

We wish to acknowledge all the work of N Pattison and L McCowan, authors of the previous version of this review.

We thank Nasreen Aflaifel for helping prepare the 'Summary of findings' tables. Nasreen Aflaifel's work was financially supported by the UNDP/UNFPA/UNICEF/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction (HRP), Department of Reproductive Health and Research (RHR), World Health Organization. The named authors alone are responsible for the views expressed in this publication.

This project was supported by the National Institute for Health Research, via Cochrane Infrastructure funding to Cochrane Pregnancy and Childbirth. The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the Systematic Reviews Programme, NIHR, NHS or the Department of Health.

Comparison 1

Comparison 3

Characteristics of included studies [ordered by study ID]

Characteristics of excluded studies [ordered by study ID]

Internal sources

• The University of Liverpool, UK.

External sources

• National Institute for Health Research, UK.

  Previous update. NIHR NHS Cochrane Collaboration Programme Grant Scheme award for NHS‐prioritised centrally‐managed, pregnancy and childbirth systematic reviews: CPGS02

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