Fetal electrocardiogram (ECG) for fetal monitoring during labour
Abstract
Background
Hypoxaemia during labour can alter the shape of the fetal electrocardiogram (ECG) waveform, notably the relation of the PR to RR intervals, and elevation or depression of the ST segment. Technical systems have therefore been developed to monitor the fetal ECG during labour as an adjunct to continuous electronic fetal heart rate monitoring with the aim of improving fetal outcome and minimising unnecessary obstetric interference.
Objectives
To compare the effects of analysis of fetal ECG waveforms during labour with alternative methods of fetal monitoring.
Search methods
The Cochrane Pregnancy and Childbirth Group's Trials Register (latest search 23 September 2015) and reference lists of retrieved studies.
Selection criteria
Randomised trials comparing fetal ECG waveform analysis with alternative methods of fetal monitoring during labour.
Data collection and analysis
One review author independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy. One review author assessed the quality of the evidence using the GRADE approach.
Main results
Seven trials (27,403 women) were included: six trials of ST waveform analysis (26,446 women) and one trial of PR interval analysis (957 women). The trials were generally at low risk of bias for most domains and the quality of evidence for ST waveform analysis trials was graded moderate to high. In comparison to continuous electronic fetal heart rate monitoring alone, the use of adjunctive ST waveform analysis made no obvious difference to primary outcomes: births by caesarean section (risk ratio (RR) 1.02, 95% confidence interval (CI) 0.96 to 1.08; six trials, 26,446 women; high quality evidence); the number of babies with severe metabolic acidosis at birth (cord arterial pH less than 7.05 and base deficit greater than 12 mmol/L) (average RR 0.72, 95% CI 0.43 to 1.20; six trials, 25,682 babies; moderate quality evidence); or babies with neonatal encephalopathy (RR 0.61, 95% CI 0.30 to 1.22; six trials, 26,410 babies; high quality evidence). There were, however, on average fewer fetal scalp samples taken during labour (average RR 0.61, 95% CI 0.41 to 0.91; four trials, 9671 babies; high quality evidence) although the findings were heterogeneous and there were no data from the largest trial (from the USA). There were marginally fewer operative vaginal births (RR 0.92, 95% CI 0.86 to 0.99; six trials, 26,446 women); but no obvious difference in the number of babies with low Apgar scores at five minutes or babies requiring neonatal intubation, or babies requiring admission to the special care unit (RR 0.96, 95% CI 0.89 to 1.04, six trials, 26,410 babies; high quality evidence). There was little evidence that monitoring by PR interval analysis conveyed any benefit of any sort.
Authors' conclusions
The modest benefits of fewer fetal scalp samplings during labour (in settings in which this procedure is performed) and fewer instrumental vaginal births have to be considered against the disadvantages of needing to use an internal scalp electrode, after membrane rupture, for ECG waveform recordings. We found little strong evidence that ST waveform analysis had an effect on the primary outcome measures in this systematic review.
There was a lack of evidence showing that PR interval analysis improved any outcomes; and a larger future trial may possibly demonstrate beneficial effects.
There is little information about the value of fetal ECG waveform monitoring in preterm fetuses in labour. Information about long‐term development of the babies included in the trials would be valuable.
PICOs
Plain language summary
Fetal electrocardiogram (ECG) for fetal monitoring during labour
Monitoring the baby's heart using electrocardiography (ECG) plus cardiotocography (CTG) during labour provides some modest help for mothers and babies when continuous monitoring is needed.
Strong uterine contractions during labour reduce the flow of maternal blood to the placenta. The umbilical cord may also be compressed during labour, especially if the membranes are ruptured. Usually the baby has sufficient reserve to withstand this effect but some may become distressed. Electronic heart monitoring may be suggested if the doctors think the baby is not getting enough oxygen during labour. Two different methods may be used. CTG measures the baby's heart rate together with the mother's uterine contractions. An ECG measures the heart's electrical activity and the pattern of the heart beats. This involves an electrode being passed through the woman's cervix and attached to the baby's head. This review of seven randomised controlled trials, including a total of 27,403 women, found that monitoring the baby using ECG plus CTG resulted in fewer blood samples needing to be taken from the baby's scalp, and less surgical assistance with the birth, than with CTG alone. There was no difference in the number of caesarean deliveries and little to suggest that babies were in better condition at birth. The evidence was found to be of high quality.
Authors' conclusions
Summary of findings
| Fetal ECG (ST analysis) plus CTG versus CTG alone for fetal monitoring during labour | ||||||
| Patient or population: Pregnant women (and their fetuses) in labour, with a perceived need for continuous electronic fetal heart rate monitoring | ||||||
| Outcomes | Anticipated absolute effects* (95% CI) | Relative effect | № of participants | Quality of the evidence | Comments | |
| Risk with CTG alone | Risk with Fetal ECG plus CTG | |||||
| Caesarean section ‐ ST analysis | Study population | RR 1.02 | 26,446 | ⊕⊕⊕⊕ | ||
| 135 per 1000 | 137 per 1000 | |||||
| Moderate | ||||||
| 119 per 1000 | 121 per 1000 | |||||
| Cord pH less than 7.05 and base deficit greater than 12 mmol/L ‐ ST analysis | Study population | RR 0.72 | 25,682 | ⊕⊕⊕⊝ | ||
| 9 per 1000 | 7 per 1000 | |||||
| Moderate | ||||||
| 11 per 1000 | 8 per 1000 | |||||
| Neonatal encephalopathy ‐ ST analysis | Study population | RR 0.61 | 26,410 | ⊕⊕⊕⊕ | ||
| 2 per 1000 | 1 per 1000 | |||||
| Moderate | ||||||
| 2 per 1000 | 1 per 1000 | |||||
| Fetal blood sampling ‐ ST analysis | Study population | RR 0.61 | 9671 | ⊕⊕⊕⊕ | ||
| 154 per 1000 | 94 per 1000 | |||||
| Moderate | ||||||
| 131 per 1000 | 80 per 1000 | |||||
| Operative vaginal delivery ‐ ST analysis | Study population | RR 0.92 | 26,446 | ⊕⊕⊕⊕ | ||
| 113 per 1000 | 104 per 1000 | |||||
| Moderate | ||||||
| 133 per 1000 | 122 per 1000 | |||||
| Admission to neonatal special care unit ‐ ST analysis | Study population | RR 0.96 | 26410 | ⊕⊕⊕⊕ | ||
| 88 per 1000 | 84 per 1000 | |||||
| Moderate | ||||||
| 55 per 1000 | 53 per 1000 | |||||
| Perinatal death ‐ ST analysis | Study population | RR 1.71 | 26,446 | ⊕⊕⊕⊕ | ||
| 0 per 1000 | 1 per 1000 | |||||
| Moderate | ||||||
| 0 per 1000 | 1 per 1000 | |||||
| *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). | ||||||
| GRADE Working Group grades of evidence | ||||||
| 1 Some heterogeneity in findings (I2 55%) | ||||||
Background
Description of the condition
Labour poses a potential threat to fetal wellbeing. The supply of oxygen to the fetus requires an adequate supply of maternal blood to the placenta, a properly functioning placenta to allow transfer of oxygen from maternal to fetal blood, and a patent umbilical vein in the umbilical cord to the fetus. Strong uterine contractions in labour stop the flow of maternal blood to the placenta with intermittent decreases in oxygenation. Most fetuses have sufficient metabolic reserve to withstand this effect but those with limited reserves, notably malnourished 'growth restricted' fetuses, may become distressed. The umbilical cord may also be compressed during labour, especially if the membranes are ruptured, which may also cause distress.
Description of the intervention
The earliest method of monitoring fetal wellbeing during labour was by using the fetal (Pinard) stethoscope intermittently to calculate the fetal heart rate. During the 1960s and 1970s, electronic systems were developed to allow monitoring of the fetal heart rate together with the mother's uterine contractions (cardiotocography (CTG)), and these have been very widely used. To monitor the heart rate, signals can be obtained from an ultrasound transducer strapped to the mother's abdomen, or from an electrode clipped into the baby's scalp. Traces of the baby's heart rate may be 'continuous' (that is, throughout labour) or intermittent. Although the mother's mobility is limited by both methods, this is obviously greater with continuous monitoring. Non‐reassuring features on a CTG trace would include unusually rapid or slow rates, a flat pattern (reduced variability), and certain types of heart rate decelerations (especially 'late' or 'severe variable' decelerations). Such observations might prompt further intervention in the form of operative delivery, or additional testing of fetal condition (see below).
A systematic review of randomised trials comparing continuous electronic fetal heart rate monitoring (CTG) and intermittent auscultation (Alfirevic 2013), showed fewer babies having neonatal convulsions after continuous monitoring (risk ratio (RR) 0.50, 95% confidence interval (CI) 0.31 to 0.80), but at the cost of increased rates of obstetric intervention in the form of caesarean section (RR 1.63, 95% CI 1.29 to 2.07) and instrumental vaginal delivery (RR 1.15, 95% CI 1.01 to 1.33). Neonatal convulsions are often, but not always, associated with hypoxic‐ischaemic encephalopathy due to hypoxaemic brain damage and may be linked to subsequent neuro‐developmental disability, including cerebral palsy. It should therefore be an important goal of obstetric care to avoid neonatal convulsions. However, it is also important to avoid unnecessary obstetric interventions.
Cardiotocographic traces may be difficult to interpret, resulting in unnecessary operative interventions, while some significant changes go unrecognised. Computerised CTG has not proved helpful during labour (Dawes 1994). Adjunctive tests have therefore been developed to be used alongside CTG, in an attempt to refine assessment of fetal wellbeing with the ultimate objective of decreasing unnecessary intervention without jeopardising fetal outcome. Fetal scalp sampling for pH or lactate estimation is the best established adjunctive technique, but it is an awkward, uncomfortable procedure for the mother and involves a stab incision in the scalp of the fetus. This has limited its appeal and pre‐empts its use in areas with a high prevalence of HIV infection. An additional drawback is that, by its nature, scalp sampling can only give intermittent information about fetal acid‐base status.
To address these challenges in intrapartum fetal monitoring, technology has been developed to monitor the fetal electrocardiographic (ECG) waveform during labour. If shown helpful to either improve fetal outcome, or decrease unnecessary intervention, or both, this has the potential advantage of providing continuous information as well as being less invasive than fetal scalp sampling (although it is not non‐invasive: requiring a signal obtained from an electrode embedded in the fetal scalp).
How the intervention might work
The fetal ECG, like the adult ECG, displays P, QRS, and T waves corresponding to electrical events in the heart during each beat. The P wave represents atrial contraction, QRS ventricular contraction, and T ventricular repolarisation. Two parts of the fetal ECG waveform have attracted attention from researchers: PR/RR relations and the ST waveform (Greene 1999). Normally there is a positive correlation between the PR interval (the time between the P wave and the R component of the QRS complex) and the RR interval, such that when the heart rate increases both PR and RR intervals shorten. In sheep experiments where the fetus was made hypoxaemic, a paradoxical effect was seen, in which the PR interval shortened despite lengthening of the RR interval ('bradycardia' or slowing of the heart rate). This led to the hypothesis that measurement of PR/RR relations might help distinguish between hypoxaemic and (less worrying) non‐hypoxaemic decelerations of the human fetal heart rate during labour, thus refining assessment of fetal wellbeing.
Repolarisation of myocardial (heart muscle) cells is very sensitive to metabolic dysfunction, and may be reflected in changes of the ST waveform. Thus, in adults with myocardial infarction or exercise‐induced angina pectoris from coronary artery disease, the ST segment may be elevated. Similar findings may be seen in fetal sheep under experimental conditions of moderate to severe hypoxaemia with an elevation of the ST segment and the T wave (Greene 1987). This change can be expressed as a ratio of T wave height to QRS height: the T/QRS ratio. Testing of a microprocessor‐based system (Rosen 1989) in observational studies in humans suggested that assessment of a combination of fetal heart rate and ST waveform changes may be clinically useful (Rosen 1991).
Why it is important to do this review
It is important for clinical and economic reasons to establish whether or not fetal ECG waveform analysis is helpful in improving fetal outcome, or decreasing unnecessary intervention, or both.
Objectives
To compare the effects of analysis of fetal electrocardiogram (ECG) waveforms during labour with alternative methods of fetal monitoring.
Methods
Criteria for considering studies for this review
Types of studies
Randomised controlled trials that compare analysis of any component of the fetal electrocardiogram (ECG) during labour with alternative fetal monitoring methods. Studies using quasi‐random methods of allocation (for example, alternation) were not included.
Types of participants
Pregnant women (and their fetuses) in labour, with a perceived need for continuous electronic fetal heart rate monitoring (for reasons, seeCharacteristics of included studies table).
Types of interventions
Any type of fetal electrocardiographic waveform analysis, alone or in combination with another method of fetal assessment.
Types of outcome measures
Primary outcomes
Maternal
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Caesarean section
Fetal
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Cord artery pH less than 7.05 and base deficit greater than 12 mmol/L
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Neonatal encephalopathy
Secondary outcomes
Maternal
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Fetal blood sampling
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Operative vaginal delivery
Fetal
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Apgar score less than seven at five minutes
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Neonatal intubation
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Admission to neonatal special care unit
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Perinatal death
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Cerebral palsy
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.
Electronic searches
The Cochrane Pregnancy and Childbirth Group’s Trials Register was searched by the Trials Search Co‐ordinator (23 September 2015).
For full search methods used to populate the Pregnancy and Childbirth Group Trials Register including the detailed search strategies for CENTRAL, MEDLINE, Embase and CINAHL; the list of handsearched journals and conference proceedings, and the list of journals reviewed via the current awareness service, please follow this link to the editorial information about the Cochrane Pregnancy and Childbirth Group in The Cochrane Library and select the ‘Specialized Register ’ section from the options on the left side of the screen.
Briefly, the Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co‐ordinator and contains trials identified from:
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monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);
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weekly searches of MEDLINE (Ovid);
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weekly searches of Embase (Ovid);
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monthly searches of CINAHL (EBSCO);
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handsearches of 30 journals and the proceedings of major conferences;
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weekly current awareness alerts for a further 44 journals plus monthly BioMed Central email alerts.
Search results are screened by two people and the full text of all relevant trial reports identified through the searching activities described above is reviewed. Based on the intervention described, each trial report is assigned a number that corresponds to a specific Pregnancy and Childbirth Group review topic (or topics), and is then added to the Register. The Trials Search Co‐ordinator searches the Register for each review using this topic number rather than keywords. This results in a more specific search set which has been fully accounted for in the relevant review sections (Included, Excluded, Awaiting Classification or Ongoing).
Searching other resources
The reference lists of retrieved studies were checked and no language or date restrictions were applied to the search.
Data collection and analysis
For the methods used when assessing the trials identified in the previous version of this review,seeNeilson 2013.
The following methods were used for this update.
Selection of studies
Jim Neilson (JPN) assessed for inclusion all the potential studies identified as a result of the search strategy.
Data extraction and management
A form was designed to extract data. For eligible studies, JPN extracted the data using the agreed form. Data were entered into Review Manager software (RevMan 2014) and checked for accuracy.
When information regarding any of the above was unclear, JPN contacted the authors of the original reports to provide further details.
Assessment of risk of bias in included studies
The risk of bias for each study was assessed by JPN, using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011).
(1) Random sequence generation (checking for possible selection bias)
The review author describes for each included study the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups.
The methods were assessed as:
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low risk (any truly random process, e.g. random number table; computer random number generator);
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high risk (any non random process, e.g. odd or even date of birth; hospital or clinic record number);
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unclear.
(2) Allocation concealment (checking for possible selection bias)
The review author describes for each included study the method used to conceal the allocation sequence to determine whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment.
The methods were assessed as:
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low risk of bias (e.g. telephone or central randomisation; consecutively numbered sealed opaque envelopes);
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high risk of bias (open random allocation; unsealed or non‐opaque envelopes, alternation; date of birth);
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unclear risk of bias.
(3.1) Blinding of participants and personnel (checking for possible performance bias)
The review author describes for each included study the methods used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. Studies were considered to be at low risk of bias if they were blinded, or if it was judged that the lack of blinding could not have affected the results. Blinding was assessed separately for different outcomes or classes of outcomes.
The methods were assessed as:
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low, high or unclear risk of bias for participants;
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low, high or unclear risk of bias for personnel.
(3.2) Blinding of outcome assessment (checking for possible detection bias)
The review author describes for each included study the methods used, if any, to blind outcome assessors from knowledge of which intervention a participant received. Blinding was assessed separately for different outcomes or classes of outcomes.
The methods used to blind outcome assessment were assessed as:
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low, high or unclear risk of bias.
(4) Incomplete outcome data (checking for possible attrition bias through withdrawals, dropouts, protocol deviations)
The review author describes for each included study, and for each outcome or class of outcomes, the completeness of data including attrition and exclusions from the analysis, including whether attrition and exclusions were reported, the numbers included in the analysis at each stage (compared with the total randomised participants), reasons for attrition or exclusion where reported, and whether missing data were balanced across groups or were related to outcomes. Where sufficient information was reported, or supplied by the trial authors, these missing data were re‐included in the analyses which were undertaken. The methods were assessed as:
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low risk of bias (less than 20% missing data);
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high risk of bias (greater than 20% missing data);
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unclear risk of bias.
(5) Selective reporting bias
The review author describes for each included study how he investigated the possibility of selective outcome reporting bias and what he found.
The methods were assessed as:
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low risk of bias (where it is clear that all of the study’s pre‐specified outcomes and all expected outcomes of interest to the review have been reported);
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high risk of bias (where not all the study’s pre‐specified outcomes have been reported; one or more reported primary outcomes were not pre‐specified; outcomes of interest are reported incompletely and so cannot be used; study fails to include results of a key outcome that would have been expected to have been reported);
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unclear risk of bias.
(6) Other sources of bias
The review author describes for each included study any important concerns about other possible sources of bias.
The review author assessed whether each study was free of other problems that could put it at risk of bias:
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low risk of other bias;
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high risk of other bias;
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unclear whether there was risk of other bias.
(7) Overall risk of bias
The review author made explicit judgements about whether studies are at high risk of bias, according to the criteria given in the Handbook (Higgins 2011). With reference to (1) to (6) above, he assessed the likely magnitude and direction of the bias and whether he considered it likely to impact on the findings. In future updates, the impact of the level of bias will be explored through undertaking sensitivity analyses ‐ seeSensitivity analysis.
Assessment of the quality of the evidence using the GRADE approach
For this update the quality of the evidence was assessed using the GRADE approach as outlined in the GRADE handbook in order to assess the quality of the body of evidence relating to the following outcomes for the main comparison, fetal ECG plus CTG versus CTG alone, relating to the ST segment.
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Caesarean section
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Cord artery pH less than 7.05 and base deficit greater than 12 mmol/L
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Neonatal encephalopathy
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Fetal blood sampling
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Operative vaginal delivery
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Admission to neonatal special care unit
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Perinatal death
GRADEpro Guideline Development Tool was used to import data from Review Manager 5.3 (RevMan 2014) in order to create a ’Summary of findings’ table. A summary of the intervention effect and a measure of quality for each of the above outcomes was produced using the GRADE approach. The GRADE approach uses five considerations (study limitations, consistency of effect, imprecision, indirectness and publication bias) to assess the quality of the body of evidence for each outcome. The evidence can be downgraded from 'high quality' by one level for serious (or by two levels for very serious) limitations, depending on assessments for risk of bias, indirectness of evidence, serious inconsistency, imprecision of effect estimates or potential publication bias.
Measures of treatment effect
Dichotomous data
For dichotomous data, results are presented as summary risk ratio with 95% confidence intervals.
Continuous data
No data were analysed as continuous data. In future updates, if appropriate, we will use the mean difference if outcomes are measured in the same way between trials. We will use the standardised mean difference to combine trials that measure the same outcome, but use different methods.
Unit of analysis issues
Cluster‐randomised trials
No cluster‐randomised trials were identified for inclusion. In future updates, cluster‐randomised trials will be included in the analyses along with individually‐randomised trials. We will adjust their standard errors using the methods described in the Handbook using an estimate of the intracluster correlation co‐efficient (ICC) derived from the trial (if possible), from a similar trial or from a study of a similar population. If ICCs are used from other sources, this will be reported and sensitivity analyses will be conducted to investigate the effect of variation in the ICC. If both cluster‐randomised trials and individually‐randomised trials are identified, the relevant information will be synthesised. It will be considered reasonable to combine the results from both if there is little heterogeneity between the study designs and the interaction between the effect of intervention and the choice of randomisation unit is considered to be unlikely.
Heterogeneity in the randomisation unit will be acknowledged and a sensitivity analysis will be performed to investigate the effects of the randomisation unit.
Cross‐over trials
If, in future updates of this review, if cross‐over trials are identified on this topic, and such trials are deemed eligible for inclusion, they will be included in the analyses with parallel group trials, using methods described by Elbourne 2002.
Dealing with missing data
For included studies, levels of attrition were noted. The impact of including studies with high levels of missing data in the overall assessment of treatment effect will be explored in future updates by using sensitivity analysis.
For all outcomes, analyses were carried out, as far as possible, on an intention‐to‐treat basis, i.e. the review author attempted to include all participants randomised to each group in the analyses, and all participants were analysed in the group to which they were allocated, regardless of whether or not they received the allocated intervention. The denominator for each outcome in each trial was the number randomised minus any participants whose outcomes were known to be missing.
Assessment of heterogeneity
Statistical heterogeneity was assessed in each meta‐analysis using the Tau², I² and Chi² statistics. Heterogeneity was regarded as substantial if the I² was greater than 30% and either the Tau² was greater than zero, or there was a low P value (less than 0.10) in the Chi² test for heterogeneity.
Assessment of reporting biases
Had there been 10 or more studies in the meta‐analysis, the review author planned to investigate reporting biases (such as publication bias) using funnel plots. In future updates, funnel plot asymmetry will be assessed visually. If asymmetry is suggested by a visual assessment, exploratory analyses will be performed to investigate it.
Data synthesis
Statistical analysis was carried out using Review Manager software (RevMan 2014). Fixed‐effect meta‐analyses were used for combining data where it was reasonable to assume that studies were estimating the same underlying treatment effect: i.e. where trials were examining the same intervention, and the trials’ populations and methods were judged sufficiently similar. If there was clinical heterogeneity, sufficient to expect that the underlying treatment effects differed between trials, or if substantial statistical heterogeneity was detected, random‐effects meta‐analysis was used to produce an overall summary, if an average treatment effect across trials was considered clinically meaningful. The random‐effects summary was treated as the average of the range of possible treatment effects and the review author discusses the clinical implications of treatment effects differing between trials. If the average treatment effect was not clinically meaningful, trials were not combined.
Where random‐effects analyses are used, the results are presented as the average treatment effect with its 95% confidence interval, and the estimates of Tau² and I².
Subgroup analysis and investigation of heterogeneity
Subgroup analysis was not carried out.
The review author carried out separate comparisons for two subgroups: based on whether the technique trialled assessed PR/RR relations or the ST segment. All outcomes were assessed in both groups of comparisons.
Sensitivity analysis
In future updates of this review, sensitivity analyses will be performed to explore outcomes with statistical heterogeneity and the effects of any assumptions made, such as the value of the ICC used for cluster‐randomised trials (if appropriate).
Results
Description of studies
A total of seven trials involving 27,403 women were identified that fulfilled the criteria for inclusion (Amer‐Wahlin 2001; Belfort 2015; Ojala 2006; Strachan 2000; Vayssiere 2007; Westerhuis 2010; Westgate 1993).
Results of the search
The updated search retrieved five new reports (four trials), one was included in this 2015 update (Belfort 2015): one was excluded (Ignatov 2012); one is awaiting classification (Gongora 2014); and one is ongoing (Bach 2012).
Included studies
Out of the seven trials included, six were based on ST analysis (UK, Sweden, France, Finland, The Netherlands, USA) and one on PR length (multi‐national). SeeCharacteristics of included studies.
Excluded studies
Five studies were excluded. Two studies were not randomised controlled trials (Hruban 2006; Janku 2006), one study report was a review article (Olofsson 2003), one study did not involve analysis of fetal ECG waveform (Ignatov 2012), and one study was reported as abstract only with insufficient detail to include data (Prieto 2008).
Risk of bias in included studies
For a summary of all 'Risk of bias' assessments, please refer to Figure 1; Figure 2.
'Risk of bias' graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.
'Risk of bias' summary: review authors' judgements about each risk of bias item for each included study.
Allocation
Included trials were at low risk of selection bias.
Blinding
Given the nature of the intervention, there was little scope for blinding women and their caregivers during labour. Blinding of observers who assessed the babies varied between studies.
Incomplete outcome data
Data were largely complete.
Selective reporting
There was no suggestion of selective reporting.
Other potential sources of bias
There was no suggestion of other biases.
Effects of interventions
Seven trials (27,403 women) were included: six trials of ST waveform analysis (26,446 women) and one trial of PR interval analysis (957 women).
Comparison: Fetal electrocardiogram (ECG) plus cardiotocography (CTG) versus CTG alone
Primary outcomes
Seven trials (27,403 women) were included: six trials of ST waveform analysis (26,446 women) and one trial of PR interval analysis (957 women). The quality of evidence for ST waveform analysis trials was moderate to strong. In comparison to continuous electronic fetal heart rate monitoring alone, the use of adjunctive ST waveform analysis made no obvious difference to primary outcomes: births by caesarean section (RR 1.02, 95% CI 0.96 to 1.08; data from 26,446 women, 6 trials), Analysis 1.1; the number of babies with severe metabolic acidosis at birth (cord arterial pH less than 7.05 and base deficit greater than 12 mmol/L) (average RR 0.72, 95% CI 0.43 to 1.20; data from 25,682 babies, 6 trials; Heterogeneity: I² = 55%, Tau² = 0.21), Analysis 1.2; or babies with neonatal encephalopathy (RR 0.61, 95% CI 0.30 to 1.22; data from 26,410 babies, 6 trials), Analysis 1.3.
Secondary outcomes
As for secondary outcomes, there were on average fewer fetal scalp samples taken during labour (average RR 0.61, 95% CI 0.41 to 0.91; data from 9671 babies, 4 trials; Heterogeneity: I² = 92%, Tau² = 0.15), although the findings were heterogeneous and there were no data from the largest and most recent trial (from the USA), Analysis 1.4; there were marginally fewer operative vaginal deliveries (RR 0.92, 95% CI 0.86 to 0.99; data from 26,446 women, 6 trials) Analysis 1.5, but no obvious difference in the number of babies with low Apgar scores at five minutes (RR 0.95, 95% CI 0.73 to 1.24; data from 15302 babies, 5 trials) Analysis 1.6; or babies requiring neonatal intubation (RR 1.37, 95% CI 0.89 to 2.11; data from 12544 babies, 2 trials) Analysis 1.7, or babies requiring admission to the special care unit (RR 0.96, 95% CI 0.89 to 1.04; data from 26,410 babies, 6 trials) Analysis 1.8. There were no differences in perinatal deaths (RR 1.71, 95% CI 0.67 to 4.33; data from 26,446 babies, 6 trials), Analysis 1.9. No trial reported on the outcome cerebral palsy.
There was little evidence that monitoring by PR interval analysis conveyed any benefit.
Discussion
Summary of main results
Overall, the ST waveform trials have shown some very modest benefits in terms of process indicators, with less obstetric interference (specifically, fetal blood sampling and operative vaginal delivery), but they have not shown substantive clinical benefits (e.g. reduced encephalopathy) among women allocated to ST waveform analysis in addition to standard cardiotocography (CTG). The ST waveform trials used different generations of the same equipment (STAN recorder, Neoventa Medical, Gothenburg, Sweden). In the UK trial (Westgate 1993), the T/QRS ratio provided the basis for identifying ST segment elevation. In the subsequent trials (Amer‐Wahlin 2001; Ojala 2006; Vayssiere 2007; Westerhuis 2010; Belfort 2015), technical developments permitted the identification of ST waveform depression as well as elevation, since the former effect has also been seen in animal studies of experimentally‐induced fetal hypoxaemia. Most trials were accompanied by regular education and training sessions for labour ward staff in both cardiotocogram and ECG waveform interpretation and these may be essential for optimal implementation.
Overall completeness and applicability of evidence
Identification of studies seems to be complete. All studies were performed in high‐income settings.
Quality of the evidence
The trials were generally at low risk of bias for most 'Risk of bias' domains. The quality of evidence as assessed using the GRADE approach (see GRADE handbook) was graded moderate to high for ST waveform analysis trials (see summary of findings Table for the main comparison). It was graded high for the following primary and secondary outcomes: caesarean section; neonatal encephalopathy; fetal blood sampling; operative vaginal delivery; admission to neonatal special care unit; and perinatal death. It was graded moderate for the following primary outcome: cord artery pH less than 7.05 and base deficit greater than 12 mmol/L. Downgrading for cord artery pH less than 7.05 and base deficit greater than 12 mmol/L was due to some heterogeneity in the findings.
Potential biases in the review process
A comprehensive search of the literature was conducted in order to minimise the possibility of publication bias. Only one review author assessed trials for inclusion and conducted data extraction and this is a potential bias of the review process. However, retrospective 'Risk of bias' assessments were conducted by more than one person (student medical statisticians) to minimise potential biases.
Agreements and disagreements with other studies or reviews
Five reported systematic reviews on this topic including four aggregate reviews (this Cochrane review included) and one individual patient data meta‐analysis (Schuit 2013) have been critiqued by Olofsson 2014.
'Risk of bias' graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.
'Risk of bias' summary: review authors' judgements about each risk of bias item for each included study.
Comparison 1 Fetal ECG plus CTG versus CTG alone, Outcome 1 Caesarean section.
Comparison 1 Fetal ECG plus CTG versus CTG alone, Outcome 2 Cord pH < 7.05 + base deficit > 12 mmol/L.
Comparison 1 Fetal ECG plus CTG versus CTG alone, Outcome 3 Neonatal encephalopathy.
Comparison 1 Fetal ECG plus CTG versus CTG alone, Outcome 4 Fetal blood sampling.
Comparison 1 Fetal ECG plus CTG versus CTG alone, Outcome 5 Operative vaginal delivery.
Comparison 1 Fetal ECG plus CTG versus CTG alone, Outcome 6 Apgar score < 7 at 5 minutes.
Comparison 1 Fetal ECG plus CTG versus CTG alone, Outcome 7 Neonatal intubation.
Comparison 1 Fetal ECG plus CTG versus CTG alone, Outcome 8 Admission neonatal special care unit.
Comparison 1 Fetal ECG plus CTG versus CTG alone, Outcome 9 Perinatal death.
| Fetal ECG (ST analysis) plus CTG versus CTG alone for fetal monitoring during labour | ||||||
| Patient or population: Pregnant women (and their fetuses) in labour, with a perceived need for continuous electronic fetal heart rate monitoring | ||||||
| Outcomes | Anticipated absolute effects* (95% CI) | Relative effect | № of participants | Quality of the evidence | Comments | |
| Risk with CTG alone | Risk with Fetal ECG plus CTG | |||||
| Caesarean section ‐ ST analysis | Study population | RR 1.02 | 26,446 | ⊕⊕⊕⊕ | ||
| 135 per 1000 | 137 per 1000 | |||||
| Moderate | ||||||
| 119 per 1000 | 121 per 1000 | |||||
| Cord pH less than 7.05 and base deficit greater than 12 mmol/L ‐ ST analysis | Study population | RR 0.72 | 25,682 | ⊕⊕⊕⊝ | ||
| 9 per 1000 | 7 per 1000 | |||||
| Moderate | ||||||
| 11 per 1000 | 8 per 1000 | |||||
| Neonatal encephalopathy ‐ ST analysis | Study population | RR 0.61 | 26,410 | ⊕⊕⊕⊕ | ||
| 2 per 1000 | 1 per 1000 | |||||
| Moderate | ||||||
| 2 per 1000 | 1 per 1000 | |||||
| Fetal blood sampling ‐ ST analysis | Study population | RR 0.61 | 9671 | ⊕⊕⊕⊕ | ||
| 154 per 1000 | 94 per 1000 | |||||
| Moderate | ||||||
| 131 per 1000 | 80 per 1000 | |||||
| Operative vaginal delivery ‐ ST analysis | Study population | RR 0.92 | 26,446 | ⊕⊕⊕⊕ | ||
| 113 per 1000 | 104 per 1000 | |||||
| Moderate | ||||||
| 133 per 1000 | 122 per 1000 | |||||
| Admission to neonatal special care unit ‐ ST analysis | Study population | RR 0.96 | 26410 | ⊕⊕⊕⊕ | ||
| 88 per 1000 | 84 per 1000 | |||||
| Moderate | ||||||
| 55 per 1000 | 53 per 1000 | |||||
| Perinatal death ‐ ST analysis | Study population | RR 1.71 | 26,446 | ⊕⊕⊕⊕ | ||
| 0 per 1000 | 1 per 1000 | |||||
| Moderate | ||||||
| 0 per 1000 | 1 per 1000 | |||||
| *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). | ||||||
| GRADE Working Group grades of evidence | ||||||
| 1 Some heterogeneity in findings (I2 55%) | ||||||
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 1 Caesarean section Show forest plot | 7 | Risk Ratio (M‐H, Fixed, 95% CI) | Subtotals only | |
| 1.1 ST analysis | 6 | 26446 | Risk Ratio (M‐H, Fixed, 95% CI) | 1.02 [0.96, 1.08] |
| 1.2 PR analysis | 1 | 957 | Risk Ratio (M‐H, Fixed, 95% CI) | 0.79 [0.61, 1.04] |
| 2 Cord pH < 7.05 + base deficit > 12 mmol/L Show forest plot | 6 | Risk Ratio (M‐H, Random, 95% CI) | Subtotals only | |
| 2.1 ST analysis | 6 | 25682 | Risk Ratio (M‐H, Random, 95% CI) | 0.72 [0.43, 1.20] |
| 2.2 PR analysis | 0 | 0 | Risk Ratio (M‐H, Random, 95% CI) | 0.0 [0.0, 0.0] |
| 3 Neonatal encephalopathy Show forest plot | 6 | Risk Ratio (M‐H, Fixed, 95% CI) | Subtotals only | |
| 3.1 ST analysis | 6 | 26410 | Risk Ratio (M‐H, Fixed, 95% CI) | 0.61 [0.30, 1.22] |
| 3.2 PR analysis | 0 | 0 | Risk Ratio (M‐H, Fixed, 95% CI) | 0.0 [0.0, 0.0] |
| 4 Fetal blood sampling Show forest plot | 5 | Risk Ratio (M‐H, Random, 95% CI) | Subtotals only | |
| 4.1 ST analysis | 4 | 9671 | Risk Ratio (M‐H, Random, 95% CI) | 0.61 [0.41, 0.91] |
| 4.2 PR analysis | 1 | 957 | Risk Ratio (M‐H, Random, 95% CI) | 0.91 [0.69, 1.19] |
| 5 Operative vaginal delivery Show forest plot | 7 | Risk Ratio (M‐H, Fixed, 95% CI) | Subtotals only | |
| 5.1 ST analysis | 6 | 26446 | Risk Ratio (M‐H, Fixed, 95% CI) | 0.92 [0.86, 0.99] |
| 5.2 PR analysis | 1 | 957 | Risk Ratio (M‐H, Fixed, 95% CI) | 0.94 [0.75, 1.17] |
| 6 Apgar score < 7 at 5 minutes Show forest plot | 6 | Risk Ratio (M‐H, Fixed, 95% CI) | Subtotals only | |
| 6.1 ST analysis | 5 | 15302 | Risk Ratio (M‐H, Fixed, 95% CI) | 0.95 [0.73, 1.24] |
| 6.2 PR analysis | 1 | 957 | Risk Ratio (M‐H, Fixed, 95% CI) | 0.42 [0.11, 1.62] |
| 7 Neonatal intubation Show forest plot | 3 | Risk Ratio (M‐H, Fixed, 95% CI) | Subtotals only | |
| 7.1 ST analysis | 2 | 12544 | Risk Ratio (M‐H, Fixed, 95% CI) | 1.37 [0.89, 2.11] |
| 7.2 PR analysis | 1 | 957 | Risk Ratio (M‐H, Fixed, 95% CI) | 0.74 [0.26, 2.11] |
| 8 Admission neonatal special care unit Show forest plot | 7 | Risk Ratio (M‐H, Fixed, 95% CI) | Subtotals only | |
| 8.1 ST analysis | 6 | 26410 | Risk Ratio (M‐H, Fixed, 95% CI) | 0.96 [0.89, 1.04] |
| 8.2 PR analysis | 1 | 957 | Risk Ratio (M‐H, Fixed, 95% CI) | 0.77 [0.45, 1.33] |
| 9 Perinatal death Show forest plot | 7 | Risk Ratio (M‐H, Fixed, 95% CI) | Subtotals only | |
| 9.1 ST analysis | 6 | 26446 | Risk Ratio (M‐H, Fixed, 95% CI) | 1.71 [0.67, 4.33] |
| 9.2 PR analysis | 1 | 957 | Risk Ratio (M‐H, Fixed, 95% CI) | 2.96 [0.12, 72.39] |
