Bayesian interpretation of trials: the example of intrapartum electronic fetal heart rate monitoring

Simplifying the language of fetal monitoring

BACKGROUND

Health professionals in Australia and New Zealand have used various intrapartum fetal surveillance (IFS) guidelines, with clear differences in how these guidelines present information. Based on clinician feedback, the 2015 Queensland Clinical Guideline on IFS structured the prose-based Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) IFS Guidelines as a traffic-light matrix and represented the categorical terms of unlikely, maybe, possible and likely fetal compromise, as the colours GREEN, BLUE, AMBER, and RED, respectively.

AIMS

To determine whether the interpretation of the RANZCOG IFS Guidelines in Table Format is more accurate and quicker compared to the current presentation of the RANZCOG Guideline in prose format.

MATERIALS AND METHOD

Twenty-nine clinicians, naïve to the use of the RANZCOG IFS Guidelines, interpreted ten cardiotocographs (CTGs) using one format and then the alternative format (totalling 580 CTG interpretations). Accuracy and time to decision were recorded as well as a participant questionnaire. A repeated measures analysis of variance was used to compare differences.

RESULTS

Compared to prose format, clinicians interpreted CTGs quicker using the table format (P < 0.01), especially CTGs representative of unlikely and maybe fetal compromise. There was a trend toward more accurate interpretation for table format for all clinicians, with significance among medical officers (P = 0.02). Participants responded more favourably to the table format regarding questions about ease of use, determining actions required, and desire to use the system in the future (P < 0.01).

CONCLUSIONS

Presenting the RANZCOG IFS Guideline in table format as opposed to prose format improved the speed and accuracy of CTG interpretation and is preferred by clinicians.

Intrauterine Growth Restriction. Guideline of the German Society of Gynecology and Obstetrics (S2k-Level, AWMF Registry No. 015/080, October 2016)

AIMS

The aim of this official guideline published and coordinated by the German Society of Gynecology and Obstetrics (DGGG) was to provide consensus-based recommendations obtained by evaluating the relevant literature for the diagnostic treatment and management of women with fetal growth restriction.

METHODS

This S2k guideline represents the structured consensus of a representative panel of experts with a range of different professional backgrounds commissioned by the Guideline Committee of the DGGG.

RECOMMENDATIONS

Recommendations for diagnostic treatment, management, counselling, prophylaxis and screening are presented.

Caesarean Section for Foetal Distress and Correlation with Perinatal Outcome

BACKGROUND

The main documented indication of intrapartum caesarean section is foetal distress (MacKenzie and Cooke in BMJ 323(7318):930, 2001). Foetal distress indicates foetal hypoxia and acidosis during intrauterine life.

PURPOSE

To correlate the diagnosis of foetal distress and perinatal outcome.

METHODS

This was a prospective observational study of women who underwent caesarean section for foetal distress as detected by cardiotocography and not responding to intrauterine resuscitation. The foetal Apgar score at 1 and 5 min was recorded and cord blood pH was measured in all cases. The neonatal outcome was studied with regard to the need for supportive ventilation and admission to NICU/nursery.

RESULTS

In our study, 14.38 % cases diagnosed with foetal distress subsequently had poor outcome. Twenty-one babies had a 5-min Apgar score <7, required immediate resuscitation and were admitted in NICU. Twelve foetuses had a 1-min Apgar score <4, while there were three cases of severe birth asphyxia (Apgar score <4 at 5 min); of these, two babies died. The neonatal outcome was poorer in cases with associated complicating factors.

CONCLUSION

The diagnosis of foetal distress is imprecise and a poor predictor of foetal outcome-the result is a tendency for unnecessary caesarean sections. On the contrary, lack of adverse outcome could reflect that our unit makes decisions at a time before clinically significant foetal compromise occurs.

Imperative for improvements and international convergence of intrapartum fetal monitoring: A bird’s eye view

Intrapartum fetal monitoring has been criticized for the lack of evidence of improvement in fetal outcome despite causing increased operative intervention. Paradoxically, cardiotocography (CTG) has been a major driver for litigation for neonatal neurological injury. This analytical review tries to explore why extensive clinical studies and trials over 50 years have failed to demonstrate or bring about significant improvement in intrapartum fetal monitoring. There seems a need for significant reform. International congruence on most aspects of CTG interpretation [definitions of fetal heart rate (FHR) parameters, CTG recording speed, 3-tier systems, etc.] is highly desirable to facilitate future meaningful clinical studies, evaluation and progress in this field. The FHR changes are non-specific and poor surrogate for fetal well-being. As a compromise for maintaining low false-negative results for fetal acidemia, a high false-positive value may have to be accepted. The need for redefining the place of adjuvant tests of fetal well-being like fetal blood sampling or fetal electrocardiography (ECG) is discussed. The FHR decelerations are often deterministic (center-stage) in CTG interpretation and 3-tier categorization. It is discussed if their scientific and physiological classification (avoiding framing and confirmation biases) may be best based on time relationship to uterine contractions alone. This may provide a more sound foundation which could improve the reliability and further evolution of 3-tier systems. Results of several trials of fetal ECG (STAN) have been inconclusive and a need for a fresh approach or strategy is considered. It is hoped that the long anticipated Computer-aided analysis of CTG will be more objective and reliable (overcome human factors) and will offer valuable support or may eventually replace visual CTG interpretation. In any case, the recording and archiving all CTGs digitally and testing cord blood gases routinely in every delivery would be highly desirable for future research. This would facilitate well designed retrospective studies which can be very informative especially when prospective randomised controlled trials are often difficult and resource-intensive.

Acceptability of the fetal electrocardiographic (STAN) monitoring system by staff at a high risk maternity unit

AIMS

To assess staff acceptability of STAN monitoring system.

METHODS

This was a prospective study of health care professionals involved in the first 18 months of STAN use at a high risk maternity unit.

RESULTS

During the study period 75% of midwives and 80% of doctors questioned felt confident when interpreting STAN cases. A total of 88% of midwives and 90% of doctors felt adequately supported in their actual clinical use of the system. Of all the obstetricians who used the STAN, 95% felt it was an acceptable alternative to fetal blood sampling. One of the main complaints was poor signal quality which occurred in 16% of cases. As many as 97% of doctors and 96% of midwives considered STAN to be an acceptable way of monitoring high risk women after its introduction.

CONCLUSIONS

Introduction of a new monitoring system to a high risk labor ward is possible, and acceptable to its staff. Constant practical and theoretical support and adherence to strict, easily understood guidelines is required.

Cesarean section for suspected fetal distress, continuous fetal heart monitoring and decision to delivery time

OBJECTIVE

To find out the efficacy of continuous fetal heart monitoring by analyzing the cases of cesarean section for nonreassuring fetal heart in labor, detected by cardiotocography (CTG) and correlating these cases with perinatal outcome. To evaluate whether a 30 minute decision to delivery (D-D) interval for emergency cesarean section influences perinatal outcome.

METHODS

This was a prospective observational study of 217 patients who underwent cesarean section at > or = 36 weeks for non-reassuring fetal heart in labor detected by CTG. The maternal demographic profile, specific types of abnormal fetal heart rate tracing and the decision to delivery time interval were noted. The adverse immediate neonatal outcomes in terms of Apgar score <7 at 5 minutes, umbilical cord thornH <7.10, neonates requiring immediate ventilation and NICU admissions were recorded. The correlation between non-reassuring fetal heart, decision to delivery interval and neonatal outcome were analyzed.

RESULTS

Out of 3148 patients delivered at > or = 36 weeks, 217 (6.8%) patients underwent cesarean section during labor primarily for non-reassuring fetal heart. The most common fetal heart abnormality was persistent bradycardia in 106 (48.8%) cases followed by late deceleration in 38 (17.5%) cases and decreased beat to beat variability in 17 (7.8%) cases. In 33 (15.2%) babies the 5 minutes Apgar score was <7 out of which 13 (5.9%) babies had cord thornH <7.10. Thirty three (15.2%) babies required NICU admission for suspected birth asphyxia. Rest 184 (84.7%) neonates were born healthy and cared for by mother. Regarding decision to delivery interval of < or =30 minutes versus >30 minutes, there was no significant difference in the incidence of Apgar score <7 at 5 minutes, cord pH <7.10 and new born babies requiring immediate ventilation. But the need for admission to NICU in the group of D-D interval < or = 30 minutes was significantly higher compared to the other group where D-D interval was >30 minutes.

CONCLUSION

Non-reassuring fetal heart rate detected by CTG did not correlate well with adverse neonatal outcome. There was no significant difference in immediate adverse neonatal outcome whether the D-D time interval was < or = 30 minutes or >30 minutes; contrary to this, NICU admission for suspected birth asphyxia in </= 30 minutes group was significantly higher.

A French randomized controlled trial of ST-segment analysis in a population with abnormal cardiotocograms during labor

OBJECTIVE

The purpose of this study was to assess whether knowledge of ST-segment analysis was associated with a reduction in operative deliveries for nonreassuring fetal status (NRFS) or with a need for at least 1 scalp pH during labor.

STUDY DESIGN

Seven hundred ninety-nine women at term with abnormal cardiotocography or meconium-stained amniotic fluid (7%) were assigned randomly to the intervention group (cardiotocography + STAN) or the control group (cardiotocography) in 2 university hospitals in Strasbourg, France. Scalp pH testing was optional in both groups. Abnormal neonatal outcome was pH <7.05 or umbilical cord blood artery base deficit of >12 or a 5-min Apgar score of <7 or neonatal intensive care unit admission or convulsions or neonatal death. Study power was 80% for the detection of a prespecified reduction from 50%-40% in operative delivery for NRFS.

RESULTS

The operative delivery (cesarean or instrumental) rate for NRFS did not differ between the 2 groups: 33.6% (134/399) in the cardiotocography + STAN analysis group vs 37% (148/400) in the cardiotocography group (relative risk, 0.91; 95% CI, 0.75-1.10). The rate of operative delivery for dystocia was also similar in both groups. The percentage of women whose fetus had at least 1 scalp pH measurement during labor was substantially lower in the group with ST-segment analysis: 27% compared with 62% (relative risk, 0.44; 95% CI, 0.36-0.52). Neonatal outcomes did not differ significantly between groups.

CONCLUSION

In a population with abnormal cardiotocography in labor, cardiotocography combined with ST-segment analysis was not associated with a reduction in operative deliveries for NRFS. The proportion of infants without scalp pH sampling during labor increased substantially, however.

A randomised clinical trial on cardiotocography plus fetal blood sampling versus cardiotocography plus ST-analysis of the fetal electrocardiogram (STAN) for intrapartum monitoring

BACKGROUND

Cardiotocography (CTG) is worldwide the method for fetal surveillance during labour. However, CTG alone shows many false positive test results and without fetal blood sampling (FBS), it results in an increase in operative deliveries without improvement of fetal outcome. FBS requires additional expertise, is invasive and has often to be repeated during labour. Two clinical trials have shown that a combination of CTG and ST-analysis of the fetal electrocardiogram (ECG) reduces the rates of metabolic acidosis and instrumental delivery. However, in both trials FBS was still performed in the ST-analysis arm, and it is therefore still unknown if the observed results were indeed due to the ST-analysis or to the use of FBS in combination with ST-analysis.

METHODS/DESIGN

We aim to evaluate the effectiveness of non-invasive monitoring (CTG + ST-analysis) as compared to normal care (CTG + FBS), in a multicentre randomised clinical trial setting. Secondary aims are: 1) to judge whether ST-analysis of fetal electrocardiogram can significantly decrease frequency of performance of FBS or even replace it; 2) perform a cost analysis to establish the economic impact of the two treatment options. Women in labour with a gestational age > or = 36 weeks and an indication for CTG-monitoring can be included in the trial. Eligible women will be randomised for fetal surveillance with CTG and, if necessary, FBS or CTG combined with ST-analysis of the fetal ECG. The primary outcome of the study is the incidence of serious metabolic acidosis (defined as pH < 7.05 and Bdecf > 12 mmol/L in the umbilical cord artery). Secondary outcome measures are: instrumental delivery, neonatal outcome (Apgar score, admission to a neonatal ward), incidence of performance of FBS in both arms and cost-effectiveness of both monitoring strategies across hospitals. The analysis will follow the intention to treat principle. The incidence of metabolic acidosis will be compared across both groups. Assuming a reduction of metabolic acidosis from 3.5% to 2.1 %, using a two-sided test with an alpha of 0.05 and a power of 0.80, in favour of CTG plus ST-analysis, about 5100 women have to be randomised. Furthermore, the cost-effectiveness of CTG and ST-analysis as compared to CTG and FBS will be studied.

DISCUSSION

This study will provide data about the use of intrapartum ST-analysis with a strict protocol for performance of FBS to limit its incidence. We aim to clarify to what extent intrapartum ST-analysis can be used without the performance of FBS and in which cases FBS is still needed.

TRIAL REGISTRATION NUMBER

ISRCTN95732366.

Use of Fetal Electrocardiogram for Intrapartum Monitoring

Introduction: Intrapartum fetal monitoring is essential for the identification of fetal hypoxia to reduce perinatal morbidity and mortality. Cardiotocography is associated with low specificity for fetal acidosis and poor perinatal outcome leading to unnecessary operative deliveries. ST waveform analysis of the fetal electrocardiogram has been shown to be a promising adjunctive intrapartum assessment tool. We aim to present the pathophysiology, the role of intrapartum monitoring and the practical usage of this relatively new technology in our review. Methods: An electronic search of Medline and OVID was carried out, followed by a manual search of the references identified by the electronic search. Results: The incorporation of ST waveform analysis to cardiotocography has been shown to reduce the rates of neonatal metabolic acidosis, moderate and severe neonatal encephalopathy, thus improving perinatal outcome. The reduction in operative delivery rates due to fetal distress is also significant. The pathophysiology and practical usage of this technology were discussed. Conclusions: With more accurate identification of fetal hypoxia and reduction of unnecessary intervention rates, incorporation of ST waveform analysis of fetal electrocardiography into cardiotocography can improve the standard of intrapartum fetal monitoring. Key words: Cardiotocography, Fetal electocardiography, Fetal ST waveform analysis, Intrapartum, Perinatal outcomes

Fetal pulse oximetry and wavelet analysis of the fetal heart rate in the evaluation of abnormal cardiotocography tracings

AIM

Previous studies indicate that the addition of wavelet analysis of the fetal pulse oximetry tracings (FSPO2) and fetal heart rate (FHR) variability to cardiotocography (CTG), for intrapartum fetal monitoring, provides useful information on the fetal response to hypoxia. We applied the new procedure in non-reassuring CTG patterns, in which cesarean section was performed, and tested its accuracy in the diagnosis of the intrapartum fetal compromise.

METHODS

At the 'Aretaieion' University Hospital labor ward, 318 women with term fetuses in the cephalic presentation entered the trial during labor. They all were monitored with external CTG and fetal pulse oximetry. In the cases that cesarean section was applied, because of abnormal CTG tracings, we applied a method based on the multiresolution wavelet analysis and a self-organized map neural network on the first and second stage of labor. The main outcome parameter was the rate of cord metabolic acidosis at birth (pH < 7.05). Secondary outcomes included Apgar scores at 5 min, fetal transmission to neonatal intensive care unit (NICU) and neonatal encephalopathy.

RESULTS

Fifty out of 318 cases delivered operatively because of abnormal CTG patterns (rate 15.72%). In 30 cases, cord pH was >7.05, while in 11 Apgar scores at 5 min were <7, while none of those neonates were transferred to NICU. In the rest 20 cases cord pH was <7.05; in all of these cases Apgar scores at 5 min were <7, while four neonates were transferred to NICU. In one of them, neonatal encephalopathy was diagnosed. After the offline application of wavelet analysis and neural networks to the pulse oximetry and FHR variability readings of the 50 cases, statistics calculated that the system showed a sensitivity of 85% and a specificity of 93%, while false negative and false positive rates were 15% and 7%, respectively.

CONCLUSION

Computerized FHR and FSPO2 monitoring shows an excellent efficacy and reliability in interpreting non-reassuring FHR recordings.

Measurement of beliefs about effectiveness of laparoscopic uterosacral nerve ablation

To explore gynaecologists' 'prior' beliefs on effectiveness of laparoscopic uterosacral nerve ablation (LUNA), a structured survey was used to gather information on the distribution of their prior beliefs regarding the effects of LUNA on pelvic pain, both numerically [on a 10-point visual analogue scale] and by responses to a questionnaire. None of the 25 gynaecologists responding to the questionnaire stated that LUNA would increase pain, while two of the 25 gave numerical answers suggesting they believed that the intervention would worsen the pain. The most widely held 'prior belief', reflected in both questionnaire and numerical responses, was that LUNA would have a small beneficial effect on pain.

Quality of intrapartum cardiotocography in twin deliveries

OBJECTIVE

Intrapartum fetal heart rate (FHR) recordings in twins were compared for fetal signal loss during both stages of labor to assess the quality of these recordings by the method that had been used: external ultrasound or directly via a scalp electrode.

STUDY DESIGN

Analysis of recordings collected between January 1, 1994, and January 1, 2002, from consecutive twin deliveries at the Vrije Universiteit Medical Center in Amsterdam. One hundred seventy-two twins that delivered via the vaginal route were included in the study. FHR recordings had a duration of at least 1 hour before the birth of the second twin. Subdivision took place on the basis of the recording technique, ie, ultrasound or scalp electrode. FHR data was obtained with HP-M1350 cardiotocographs. The status (pen on, pen off, maternal signal) and the mode of the signals were acquired. The duration of pen lifts and maternal signals was divided by the total duration of the recording. Statistical analyses were performed with the Mann-Whitney U test and the Wilcoxon signed ranks test.

RESULTS

Recordings obtained via ultrasound demonstrated significantly more fetal signal loss than those obtained via the direct mode, particularly in the second stage. Approximately 26% to 33% of first stage and 41% to 63% of second stage ultrasound intrapartum FHR recordings in twins exceeded the International Federation of Gynecology and Obstetrics (FIGO) criteria for fetal signal loss.

CONCLUSION

Intrapartum FHR monitoring via ultrasound provides far poorer quality FHR signals than the direct mode. The direct mode deserves a more prominent position in fetal surveillance than it currently has.

Management of fetal growth restriction

When fetuses are growth restricted as a result of inadequate placental function, there is an increased risk of poor perinatal outcome compared with fetuses where small dimensions are constitutional and associated with normal placental function. The management of reduced fetal size should therefore focus on the identification of the fetus at risk due to placental dysfunction, and longitudinal assessment to reduce the morbidity and mortality associated with this pathology by ideal timing of delivery. The aim of this review is to rationalize the best way to assess fetuses affected in this way and how to improve their outcome by appropriately timed intervention.

Current status of intrapartum fetal monitoring: cardiotocography versus cardiotocography + ST analysis of the fetal ECG

Two randomized controlled trials (RCT) on intrapartum fetal monitoring with cardiotocography (CTG) only versus CTG combined with automatic ST segment waveform analysis of the fetal ECG have been performed. In altogether 6826 randomized cases, the odds ratio for operative delivery for fetal distress (ODFD) was 0.65 (95% confidence interval 0.53-0.78) and for metabolic acidosis at birth 0.39 (0.21-0.72), in favor of the CTG+ST method. CTG combined with ST analysis increases the ability of obstetricians to identify fetal hypoxia and to intervene more appropriately, resulting in an improved perinatal outcome.

Generalized synthesis of evidence and the threat of dissemination bias. the example of electronic fetal heart rate monitoring (EFM)

Assessment of the potential impact of dissemination bias is necessary for meta-analysis. When evidence is available from studies of different designs, the different study types may be affected by dissemination bias to differing degrees. The evidence relating to electronic fetal heart rate monitoring (EFM) for preventing perinatal mortality is used to explore the feasibility of carrying out a dissemination bias assessment in a generalized synthesis of evidence (gse) framework. Visual inspection of funnel plots, statistical tests, and methods to "adjust" the results of a meta-analysis are all used in an extensive sensitivity analysis. The potential impact of dissemination bias on gse models synthesizing all the evidence together is also reported. Detailed consideration is given to the influence of meta-analysis model choice, and outcome scale used. Using the risk difference scale, funnel plots of the observational studies appeared highly asymmetric. However, further explorations show these conclusions are not robust over use of different outcome measures or different meta-analysis models. Researchers should be aware that dissemination bias may affect different sources of evidence differently. Although assessments such as those described here are recommended, awareness of their lack of robustness to outcome scale and model choice is important. Further research into methods to assess dissemination bias that are invariant to these factors is needed.

Cardiotocography only versus cardiotocography plus ST analysis of fetal electrocardiogram for intrapartum fetal monitoring: a Swedish randomised controlled trial

BACKGROUND

Previous studies indicate that analysis of the ST waveform of the fetal electrocardiogram provides information on the fetal response to hypoxia. We did a multicentre randomised controlled trial to test the hypothesis that intrapartum monitoring with cardiotocography combined with automatic ST-waveform analysis results in an improved perinatal outcome compared with cardiotocography alone.

METHODS

At three Swedish labour wards, 4966 women with term fetuses in the cephalic presentation entered the trial during labour after a clinical decision had been made to apply a fetal scalp electrode for internal cardiotocography. They were randomly assigned monitoring with cardiotocography plus ST analysis (CTG+ST group) or cardiotocography only (CTG group). The main outcome measure was rate of umbilical-artery metabolic acidosis (pH <7.05 and base deficit >12 mmol/L). Secondary outcomes included operative delivery for fetal distress. Results were first analysed according to intention to treat, and secondly after exclusion of cases with severe malformations or with inadequate monitoring.

FINDINGS

The CTG+ST group showed significantly lower rates of umbilical-artery metabolic acidosis than the cardiotocography group (15 of 2159 [0.7%] vs 31 of 2079 [2%], relative risk 0.47 [95% CI 0.25-0.86], p=0.02) and of operative delivery for fetal distress (193 of 2519 [8%] vs 227 of 2447 [9%], 0.83 [0.69-0.99], p=0.047) when all cases were included according to intention to treat. The differences were more pronounced after exclusion of 291 in the CTG+ST group and 283 in the CTG group with malformations or inadequate recording.

INTERPRETATION

Intrapartum monitoring with cardiotocography combined with automatic ST-waveform analysis increases the ability of obstetricians to identify fetal hypoxia and to intervene more appropriately, resulting in an improved perinatal outcome.

Bayesian methods in meta-analysis and evidence synthesis

This paper reviews the use of Bayesian methods in meta-analysis. Whilst there has been an explosion in the use of meta-analysis over the last few years, driven mainly by the move towards evidence-based healthcare, so too Bayesian methods are being used increasingly within medical statistics. Whilst in many meta-analysis settings the Bayesian models used mirror those previously adopted in a frequentist formulation, there are a number of specific advantages conferred by the Bayesian approach. These include: full allowance for all parameter uncertainty in the model, the ability to include other pertinent information that would otherwise be excluded, and the ability to extend the models to accommodate more complex, but frequently occurring, scenarios. The Bayesian methods discussed are illustrated by means of a meta-analysis examining the evidence relating to electronic fetal heart rate monitoring and perinatal mortality in which evidence is available from a variety of sources.

Hierarchical models in generalized synthesis of evidence: an example based on studies of breast cancer screening

Evidence regarding the potential benefits of a particular health care intervention is often available from a variety of disparate sources. However, formal synthesis of such evidence has traditionally concentrated almost exclusively on that derived from randomized studies, although for a range of conditions the randomized evidence will be less than adequate due to economic, organizational or ethical considerations. In such situations a formal synthesis of the evidence that is available from observational studies can be valuable whilst awaiting higher quality evidence from randomized trials. Consideration of randomized studies alone may be appropriate when assessing the efficacy of an intervention, but assessment of the effectiveness of such an intervention within a more general target population may be improved by consideration of evidence from non-randomized studies as well. Standard meta-analysis methods may allow for both within- and between-study heterogeneity; however when multiple sources of evidence are considered an extra level of complexity is introduced, namely study type. One possible solution to the problem of making inferences, particularly regarding an overall population effect, in such situations is to model the heterogeneity, both quantitative and qualitative, using a Bayesian hierarchical model. The hierarchical nature of such models specifically allows for the quantitative within and between sources of heterogeneity, whilst the Bayesian approach can accommodate a priori beliefs regarding qualitative differences between the various sources of evidence. The use of such methods in practice is illustrated in the context of screening for breast cancer; in this example evidence is available from both randomized clinical trials and observational studies. A particular appeal of a Bayesian approach for this type of problem lies in the prediction of future benefits likely to be observed in a target population. This approach to health service monitoring in general is discussed.