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.
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), 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 cardiotocography 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 (cardiotocography) and intermittent auscultation (Alfirevic 2006) 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 1.66, 95% CI 1.30 to 2.13) and instrumental vaginal delivery (RR 1.16, 95% CI 1.01 to 1.32). 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 intervention.
Cardiotocographic traces may be difficult to interpret, resulting in unnecessary operative intervention, while some significant changes go unrecognised. Computerised cardiotocography has not proved helpful during labour (Dawes 1994). However, there is some evidence that fetal blood sampling, as an adjunctive test along with cardiotocography, may decrease unnecessary intervention without jeopardising fetal outcome. No clinical trials have directly compared fetal monitoring by cardiotocography alone versus cardiotocography with the option of fetal scalp sampling. However, trials comparing cardiotocography with intermittent auscultation show a greater increase in caesarean section rates when fetal scalp sampling was not available (RR 1.79, 95% CI 1.41 to 2.27) than when available (RR 1.26, 95% CI 1.05 to 1.51) (Alfirevic 2006). Scalp sampling 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).
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).
To compare the effects of analysis of fetal electrocardiogram waveforms during labour with alternative methods of fetal monitoring.
Criteria for considering studies for this review
Types of studies
Randomised controlled trials that compare analysis of any component of the fetal electrocardiographic (ECG) during labour with alternative fetal monitoring methods. Studies using less robust 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, see Characteristics 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
- Caesarean section
- Cord artery pH less than 7.05 and base deficit greater than 12 mmol/L (blood)
- Neonatal encephalopathy
- Fetal blood sampling
- Operative vaginal delivery
- Apgar score less than seven at five minutes
- Neonatal intubation
- Admission to neonatal special care unit
- Perinatal death
- Cerebral palsy
Search methods for identification of studies
The Trials Search Co-ordinator searched the Cochrane Pregnancy and Childbirth Group’s Trials Register (12 February 2013).
The Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co-ordinator and contains trials identified from:
- monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);
- weekly searches of MEDLINE;
- weekly searches of EMBASE;
- handsearches of 30 journals and the proceedings of major conferences;
- weekly current awareness alerts for a further 44 journals plus monthly BioMed Central email alerts.
Details of the search strategies for CENTRAL, MEDLINE and EMBASE, the list of handsearched journals and conference proceedings, and the list of journals reviewed via the current awareness service can be found in the ‘Specialized Register’ section within the editorial information about the Cochrane Pregnancy and Childbirth Group.
Trials identified through the searching activities described above are each assigned to a review topic (or topics). The Trials Search Co-ordinator searches the register for each review using the topic list rather than keywords.
No language restrictions were applied.
Data collection and analysis
For the methods used when assessing the trials identified in the previous version of this review, see Appendix 1.
No new trials were identified for this update (2013). The following methods were used for the 2011 and 2012 updates and will be used in future updates.
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 2011) 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) Sequence generation (checking for possible selection bias)
For each included study the method used to generate the allocation sequence is described in sufficient detail to allow an assessment of whether it should produce comparable groups.
The methods were assessed as:
- low risk (any truly random process, e.g. random number table; computer random number generator);
- high risk (any non random process, e.g. odd or even date of birth; hospital or clinic record number);
(2) Allocation concealment (checking for possible selection bias)
For each included study the method used to conceal the allocation sequence is described to determine whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment.
The methods were assessed as:
- low risk of bias (e.g. telephone or central randomisation; consecutively numbered sealed opaque envelopes);
- high risk of bias (open random allocation; unsealed or non-opaque envelopes, alternation; date of birth);
- unclear risk of bias.
(3) Blinding (checking for possible performance bias)
For each included study the methods used, if any, to blind study participants and personnel from knowledge of which intervention a participant received are described. Studies were considered to be at low risk of bias if they were blinded, or 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:
- low, high or unclear risk of bias for participants;
- low, high or unclear risk of bias for personnel;
- low, high or unclear risk of bias for outcome assessors.
(4) Incomplete outcome data (checking for possible attrition bias through withdrawals, dropouts, protocol deviations)
For each included study, and for each outcome or class of outcomes, the completeness of data including attrition and exclusions from the analysis is described, 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, this missing data was re-included in the analyses which were undertaken. The methods were assessed as:
- low risk of bias (less than 20% missing data);
- high risk of bias (greater than 20% missing data);
- 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:
- 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);
- 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);
- unclear risk of bias.
(6) Other sources of bias
For each included study, the review author describes 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:
- low risk of other bias;
- high risk of other bias;
- 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 - see Sensitivity analysis.
Measures of treatment effect
For dichotomous data, results are presented as summary risk ratio with 95% confidence intervals.
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 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.
If, in future updates of this review, 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 T², I² and Chi² statistics. Heterogeneity was regarded as substantial if I² was greater than 30% and either T² 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
If there were 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 were performed to investigate it.
Statistical analysis was carried out using Review Manager software (RevMan 2011). 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. A random-effects summary was treated as the average 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 T² 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.
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).
Description of studies
Six trials were identified that fulfilled the criteria for inclusion: five based on ST analysis (UK, Sweden, France, Finland, Netherlands) and one on PR length (multi-national). See Characteristics of included studies.
Risk of bias in included studies
All trials employed adequate methods of allocation concealment.
Effects of interventions
Six trials (16,295 women) were included: five trials of ST waveform analysis (15,338 women) and one trial of PR interval analysis (957 women).
In comparison to continuous electronic fetal heart rate monitoring alone, the use of adjunctive ST waveform analysis made no significant difference to primary outcomes, namely births by caesarean section (risk ratio (RR) 0.99, 95% confidence interval (CI) 0.91 to 1.08), Analysis 1.1, or 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) (RR 0.78, 95% CI 0.44 to 1.37, data from 14,574 babies), Analysis 1.2, or babies with neonatal encephalopathy (RR 0.54, 95% CI 0.24 to 1.25), Analysis 1.3.
As for secondary outcomes, there were on average fewer fetal scalp samples taken during labour (RR 0.61, 95% CI 0.41 to 0.91), Analysis 1.4, although the findings were heterogeneous; there were fewer operative vaginal deliveries (RR 0.89, 95% CI 0.81 to 0.98), Analysis 1.5, and admissions to special care unit (RR 0.89, 95% CI 0.81 to 0.99), Analysis 1.8; there was no statistically significant difference in the number of babies with low Apgar scores at five minutes or babies requiring neonatal intubation, Analysis 1.6; Analysis 1.7.
There was little evidence that monitoring by PR interval analysis conveyed any benefit.
Overall, the ST waveform trials have shown some benefits in terms of process indicators with less obstetric interference (specifically, fetal blood sampling and operative vaginal delivery) and fewer babies admitted to special care units but they have not shown substantive clinical benefits (e.g. reduced encephalopathy) among women allocated to ST waveform analysis in addition to standard cardiotocography. 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), 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.
Implications for practice
These findings provide some modest support for the use of fetal ST waveform analysis when a decision has been made to undertake continuous electronic fetal heart rate monitoring during labour. However, in most labours, technically satisfactory cardiotocographic traces can be obtained by external ultrasound monitors which are less invasive than internal scalp electrodes (which are required for electrocardiographic (ECG) analysis). The scalp electrode also cannot be used if the membranes are intact. One trial of fetal ECG analysis (Amer-Wahlin 2001) used guidelines for clinicians that recommended no action if cardiotocography was normal, regardless of ST waveform analyses. A better approach to incorporation into clinical practice might be to consider fetal ECG waveform analysis (of the ST waveform) only if cardiotocography showed disquieting features.
Implications for research
The point estimates for effects of PR analysis are similar to those from the much larger ST studies, and the possibility of demonstrating beneficial effects from a larger PR trial could not be discounted. 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.
The National Institute for Health Research (NIHR) is the largest single funder of the Cochrane Pregnancy and Childbirth Group. The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the NIHR, NHS or the Department of Health.
Data and analyses
- Top of page
- Authors' conclusions
- Data and analyses
- What's new
- Contributions of authors
- Declarations of interest
- Sources of support
- Differences between protocol and review
- Index terms
Appendix 1. Methods used to assess trials included in previous versions of this review
Reports of identified trials that appeared relevant to the objectives of the review were evaluated for inclusion. Both published and unpublished reports could be included. Attempts were made, where necessary, to translate identified, non-English language reports. Primary authors were contacted for additional details when necessary. Reasons for excluding apparently relevant trials were made explicit.
Included trials were assessed according to the following criteria:
- adequate concealment of treatment allocation (for example, sealed, opaque, numbered envelopes);
- method of allocation to treatment (for example, by computer randomisation, random number tables);
- adequate documentation of how exclusions were handled after treatment allocation - to facilitate 'intention-to-treat' analyses;
- adequate blinding of outcome assessment, where appropriate;
- losses to follow-up (trials with losses of more than 25% were excluded).
Data were entered directly from reports into Review Manager software (RevMan 2011) and statistical analyses performed. For dichotomous data, risk ratios and 95% confidence intervals (CIs) were calculated. Mean differences and 95% CIs were calculated for continuous data.
Heterogeneity between trials was tested using a standard chi-squared test. In the presence of significant heterogeneity, a sensitivity analysis explored the influence of high quality trials (fulfilling the criteria above) compared to those of lesser quality.
For ease of presentation, subgroup analyses were based on trials that used analysis of ST waveforms and of PR intervals.
Last assessed as up-to-date: 12 February 2013.
Protocol first published: Issue 2, 1997
Review first published: Issue 2, 1997
Contributions of authors
JP Neilson has prepared and maintained the review.
Declarations of interest
Sources of support
- The University of Liverpool, UK.
- No sources of support supplied
Differences between protocol and review
Medical Subject Headings (MeSH)
*Labor, Obstetric; Acidosis [epidemiology]; Cardiotocography [*methods]; Cesarean Section [statistics & numerical data]; Electrocardiography [*methods]; Heart Rate, Fetal [*physiology]; Randomized Controlled Trials as Topic; Uterine Contraction [physiology]
MeSH check words
Female; Humans; Pregnancy
* Indicates the major publication for the study