Intrapartum care
DOI: 10.1111/j.1471-0528.2011.03003.x
www.bjog.org
Knowledge of adverse neonatal outcome alters
clinicians’ interpretation of the intrapartum
cardiotocograph
D Ayres-de-Campos,a,b,c D Arteiro,b C Costa-Santos,d J Bernardesa,b,c
a
Department of Obstetrics and Gynecology, Faculty of Medicine, University of Porto b Department of Obstetrics and Gynecology, Sao Joao
Hospital c INEB – Institute of Biomedical Engineering, University of Porto and d Department of Biostatistics and Medical Informatics,
Faculty of Medicine, University of Porto, Porto, Portugal
Correspondence: Prof D Ayres-de-Campos, Departmento de Ginecologia e Obstetrı́cia, Faculdade de Medicina do Porto, 4200-309 Porto,
Portugal. Email [email protected]
Accepted 8 March 2011. Published Online 24 May 2011.
Objective To evaluate the impact of knowledge of neonatal
Main outcome measures The incidence of individual fetal heart
outcome on clinicians’ interpretation of the intrapartum
cardiotocograph (CTG).
rate feature identification and tracing classification, before and
after neonatal outcome was made available.
Design Prospective evaluation of pre-recorded cases.
Results In the group with pH < 7.05, repetitive decelerations and
reduced variability were more common in the second round
(P < 0.001 and P = 0.001, respectively), as was a pathological
classification (P = 0.002); variable decelerations were less common
(P = 0.008). In the group with normal pH, less tracings in the
second round had prolonged decelerations (P = 0.013) and no
accelerations (P = 0.013), but more had pronounced decelerations
(P = 0.031) and reduced variability (P = 0.007); there was a
reduction in pathological classifications, but this difference failed
to reach statistical significance (P = 0.051).
Setting Five maternity hospitals.
Population From a database of intrapartum CTGs acquired with a
scalp electrode in singleton near-term fetuses, 20 tracings were
sequentially selected from cases with newborn umbilical artery
pH < 7.05 and 20 from cases with pH > 7.20.
Methods Five experienced obstetricians practising in different
maternity hospitals were asked to analyse the 40 tracings
individually, according to the International Federation of
Gynaecology and Obstetrics guidelines. In a first round, clinicians
were given no information on neonatal outcome. In a second
round, carried out 2 months later, clinicians were asked to analyse
the same tracings, but the order was randomly altered and
information on the newborn’s arterial pH was provided.
Clinicians were not informed of the purpose of the study or
whether the tracings were the same.
Conclusions A knowledge of adverse neonatal outcome leads to
a more severe classification of the intrapartum CTG, which
derives mainly from the evaluation of decelerations and
variability.
Keywords Agreement, cardiotocography, fetal, fetal hypoxia, fetal
monitoring, heart rate.
Please cite this paper as: Ayres-de-Campos D, Arteiro D, Costa-Santos C, Bernardes J. Knowledge of adverse neonatal outcome alters clinicians’ interpretation
of the intrapartum cardiotocograph. BJOG 2011;118:978–984.
Introduction
Intrapartum asphyxia is responsible for an important number of perinatal deaths and long-term sequelae,1 and
reviews carried out in the context of confidential enquiries
have shown that problems related to cardiotocograph
(CTG) interpretation are frequently reported.2 Retrospective analysis of CTG tracings also assumes an important
role in situations involving insurance payments or malpractice claims, where adverse outcome is usually the rule. Case
978
reviews within hospital departments or at regional medical
boards, or even in a research context,3–5 also frequently
focus on cases with poor perinatal outcome. In all these
settings, a failure or delay in reacting to CTG changes
judged to be suggestive of hypoxia is a common finding.2–6
However, it is possible that the a posteriori analysis is
influenced by the existing knowledge of adverse outcome.
In a technology in which poor intra- and inter-observer
agreement on interpretation has been consistently demonstrated in the past,7–9 it is possible that a knowledge of
ª 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology ª 2011 RCOG
Knowledge of neonatal outcome and CTG interpretation
adverse perinatal outcome has a unidirectional effect on
this phenomenon, leading to a consistently more severe
interpretation. In other areas of medicine, a knowledge of
adverse outcome has been shown to have a negative influence on reviewers’ opinions over the appropriateness of
care.10
The implications of this phenomenon in medical–legal
cases, as well as in clinical and research settings, are extremely relevant. A negative a posteriori evaluation of clinical
judgements has consequences that can go beyond the loss
of personal self-esteem and a decrease in motivation to
enter the economical and legal realms.
The aim of this study was to evaluate the impact of prior
knowledge of neonatal outcome on clinicians’ interpretation and classification of the intrapartum CTG. The International Federation of Gynaecology and Obstetrics (FIGO)
guidelines for CTG interpretation11 were used for this purpose, as they represent the largest international consensus
effort in this area, and are still widely used throughout the
world.
Population and methods
A database of intrapartum CTG tracings, acquired during a
previously reported trial,12 was sequentially searched in
order to select cases with a duration of at least 90 minutes
and with an interval between tracing end and birth of less
than 20 minutes. Participants in this study were women
with singleton fetuses, in cephalic presentation, in active
labour at more than 36 completed gestational weeks and in
whom a clinical decision was made to apply a fetal scalp
electrode and external tocodynamometer for continuous
fetal monitoring, using the STAN 21 monitor (Neoventa
Medical, Gothenburg, Sweden). Monitoring with STAN
21 was the preferred method of surveillance in high-risk
pregnancies, women with suspicious or abnormal external
cardiotocography, induced or augmented labour, meconium-stained amniotic fluid or epidural analgesia. Local
research ethics committee approval was obtained for the
trial, and all participating women signed a written
informed consent allowing their data to be used for
research purposes. Only anonymised data and CTG tracings
were used in the present study; no ST information was
made available.
As no previous data were available to estimate the sample size needed for this study, a pragmatic approach was
chosen, selecting the maximum number of cases that
observers were thought to be capable of analysing in a single session.
All selected cases had valid paired umbilical blood gas
results,13 performed within 30 minutes of birth. Twenty
tracings were sequentially selected from cases with newborn
umbilical artery pH <7.05 and 20 from cases with arterial
pH >7.20. The order by which tracings were presented to
clinicians was determined by computer-generated randomisation.
The last 90 minutes of the 40 CTG tracings were sent by
email to five obstetricians who had between 9 and 27 years
(9, 18, 20, 22 and 27 years) of experience in labour ward
management, and were practising in five different maternity hospitals. Two had previously been expert witnesses in
court cases. They were requested to fill in a questionnaire
(Figure 1) with their evaluation of CTG features and general classification of tracings according to FIGO guidelines.11 These guidelines were regularly used in their
centres, and they were also supplied with the tracings.
Clinicians were informed that tracings had been acquired
in term singleton pregnancies, but no explanation was
given with regard to the study’s purpose. The tracings contained the last 90 minutes of recording before birth, and
were printed at a paper speed of 1 cm/minute (Figure 1).
In the first round, clinicians were asked to evaluate the
40 tracings individually, with no information on neonatal
outcome. Two months later, the order of the tracings was
altered, using computer-generated randomisation, and the
clinicians were asked to evaluate the same 40 tracings, but
this time each case contained information on the newborn’s umbilical artery pH (pH < 7.05 or pH > 7.20).
Clinicians were again not informed of the purpose of the
study; nor were they told whether or not the second set of
tracings was the same as the first. The FIGO guidelines
were once more supplied.
Statistical analysis
To compare the differences between the two rounds with
regard to the identification of fetal heart rate baseline,
accelerations, decelerations, variability and overall tracing
classification, the McNemar and McNemar–Bowker tests
were used. Significance was set at P < 0.05.
Results
All tracings were evaluated by all five clinicians in both
rounds, giving a total of 400 analyses. Table 1 displays the
identification of individual CTG features (baseline, accelerations, decelerations, variability), and Table 2 displays tracing classification by the clinicians in both rounds.
In the group with umbilical artery pH <7.05, a significantly larger number of repetitive decelerations (P < 0.001)
and reduced variability (P = 0.001) were identified in the
second round, together with a decreased identification of
variable decelerations (P = 0.008). Clinicians changed their
overall tracing classification 42 times, 33 (79%) times to a
more severe class (including one change from normal to
pathological). A significantly larger number of pathological
classifications were observed when clinicians were informed
ª 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology ª 2011 RCOG
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Ayres-de-Campos et al.
Newborn: umbilical artery pH < 7.05
CASE 1
220
200
180
160
1. FHR baseline:
Normal
140
Tachycardia
Bradycardia
120
2. Presence of ≥ 2 accelerations?
100
80
40
100
80
Yes
No
3. Presence of decelerations?
60
40
20
0
220
200
Yes
23 :40
23 :45
23:50
23:55
00:00
00:05
00: 10
00: 15
No
00: 20
Variable
Repetitive
Peronounced
180
Prolonged
160
Late
140
120
4. Variability:
100
80
60
100
80
Normal
Increased
Reduced
5. Overall CTG classification:
60
40
20
0
Normal
00 :25
00:30
00:35
00:40
00 :45
00:50
01: 00
00:55
Pathological
Suspicious
01 :05
Figure 1. Example of one of the tracings and the evaluation questionnaire for the second round (containing information on the newborn’s umbilical
artery pH). CTG, cardiotocograph; FHR, fetal heart rate.
Table 1. Identification of fetal heart rate features by the five obstetricians in the two rounds. The first and second round columns display the
number of tracings in which the feature was identified by the observers. The statistical significance of the differences between the two rounds
was evaluated using McNemar* or McNemar–Bowker** tests. P values reaching statistical significance are highlighted in bold.
pH < 7.05
(20 tracings · 5 analyses · 2 rounds)
Normal baseline
Tachycardia
Bradycardia
No accelerations
Decelerations
Variable
Pronounced
Repetitive
Prolonged
Late
Normal variability
Reduced variability
Increased variability
1st round
(20 tracings ·
5 analyses)
2nd round
(20 tracings ·
5 analyses)
69
24
7
53
100
66
19
41
18
18
79
18
3
62
31
7
48
100
51
24
69
18
15
64
35
1
P
0.362à
that the newborn umbilical artery pH was <7.05 (P =
0.002).
In the group with normal pH, less tracings in the second
round were identified as having no accelerations
980
pH > 7.20
(20 tracings · 5 analyses · 2 rounds)
0.332*
–
0.008*
0.442*
<0.001*
1.000*
0.607*
0.001à
–
1st round
(20 tracings ·
5 analyses)
2nd round
(20 tracings ·
5 analyses)
73
20
7
51
96
72
13
41
16
7
92
8
0
76
19
5
40
98
76
23
48
5
3
81
19
0
P
0.574à
0.013*
0.500*
0.523*
0.031*
0.296*
0.013*
0.219*
0.007à
–
(P = 0.013) and prolonged decelerations (P = 0.013), but
more tracings were identified as having pronounced decelerations (P = 0.031) and reduced variability (P = 0.007).
Clinicians changed their overall classifications 46 times,
ª 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology ª 2011 RCOG
Knowledge of neonatal outcome and CTG interpretation
Table 2. Overall cardiotocograph (CTG) classification by the five obstetricians in the two rounds. The first and second round columns display the
number of tracings in which the classification was attributed by the observers. The statistical significance of the differences between the two
rounds was evaluated using the McNemar–Bowker test. P values reaching statistical significance are highlighted in bold.
pH < 7.05
(20 tracings · 5 analyses · 2 rounds)
1st round
2nd round
(20 tracings · 5 analyses) (20 tracings · 5 analyses)
Normal
Suspicious
Pathological
7
46
47
2
29
69
pH > 7.20
(20 tracings · 5 analyses · 2 rounds)
P
1st round
2nd round
(20 tracings · 5 analyses) (20 tracings · 5 analyses)
24 of which (52%) times to a less severe class (including
two changes from pathological to normal). Although there
was a reduction in the classification of tracings as pathological, this difference failed to reach statistical significance
(P = 0.051).
Discussion
The knowledge of a low umbilical artery pH led to a significantly increased identification of abnormal CTG features,
such as repetitive decelerations and reduced variability, as
well as to a significantly larger number of tracings being
classified as pathological. We did not establish an opposite
effect in cases with a normal pH.
Repeated evaluation of the same tracings by the same clinicians ensures that the differences observed between
rounds are a result of different interpretations, most probably conditioned by the new information provided. The
availability of real neonatal outcomes also ensures that
results can be generalised to real clinical situations. The relatively large number of cases analysed in each round, the
2-month interval between rounds and the different
sequence of tracings presented to clinicians seem to have
been sufficient to avoid recall bias, as all clinicians stated
that they were unaware of having evaluated the same tracings twice.
As far as we are aware, this is the first study to demonstrate an impact of the knowledge of neonatal outcome on
the interpretation of the intrapartum CTG. Figueras et al.14
evaluated the effect of a knowledge of a fictitious perinatal
outcome on the interpretation of 100 CTG tracings
obtained before labour, in a mixed low- and high-risk population, by an experienced midwife and a junior resident.
A significantly different evaluation of the baseline, variability, accelerations and decelerations was found between cases
with an alleged normal and an alleged adverse neonatal
outcome. Zain et al.15 selected ten intrapartum CTGs of
good signal quality, which were considered to involve an
0.002à
15
46
39
9
60
31
P
0.051à
important judgment by the managing obstetrician with
regard to the route and timing of delivery. Thirty-six obstetricians reviewed these cases, blind to the study’s objective
and, 1 month later, re-evaluated the same tracings, with
identical clinical information, but with a sham opposite
neonatal outcome. No significant differences were found in
the identification of reduced variability or late decelerations
(using no predefined interpretation criteria) when the
alleged neonatal outcome was poor, but there was a significantly larger number of opinions that there was evidence
of fetal hypoxia (P = 0.07) and that obstetricians had made
an incorrect decision (P < 0.001). Almström et al.16 demonstrated that the knowledge of normal umbilical artery
Doppler velocimetry in small-for-gestational-age fetuses
influenced the way in which clinicians interpreted intrapartum CTGs, and subsequently managed labour. When a
knowledge of a normal Doppler velocimetry was available,
only eight of 121 CTG tracings were considered to be
abnormal, whereas this occurred in 18 of the same tracings
when Doppler data were unavailable.
In our study, there was a high percentage of decelerations identified in cases with both low and normal umbilical artery pH, and a small number of tracings were
classified as normal; this can perhaps be explained by the
high-risk population included, the use of combined
CTG + ST monitoring during the second stage and the
study’s low caesarean section rate (under 5%). However, it
also suggests that the FIGO classification has a limited
capacity to discriminate between normal and acidaemic
fetuses,17 possibly related to the subjective definitions of
many CTG features, such as the various types of deceleration,18 which have a direct impact on overall tracing classification.
The lack of definition of the several types of decelerations considered in the FIGO guidelines may also have
contributed to the differences between rounds in the identification of this parameter, even in cases with normal
umbilical artery pH. It is possible that clinicians identified
ª 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology ª 2011 RCOG
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Ayres-de-Campos et al.
a larger number of pronounced decelerations in the second
round, because they attributed less clinical significance to
this entity. Less clear is the reason why they also identified
more normal pH cases as having decreased variability in
the second round. One possible explanation for this is that
observers, when presented with neonatal outcome, suspected that the study would be evaluating their predictive
capacity, and therefore analysed tracing features more
strictly and with greater care.
Cases were selected for this study in order to illustrate
the point of observer bias, and the resulting prevalence of
low umbilical artery pH is much higher than that observed
in everyday clinical practice. Results cannot therefore be
extrapolated to this setting. However, similar prevalences
may be found in confidential enquiries, case reviews and
court cases.
The findings of the present study have important implications in medical–legal, clinical and research settings. CTG
interpretation continues to play a major role in labour
ward care, and intrapartum hypoxia remains a leading
cause of obstetrical litigation, where tracing review is frequently the key element.19–21 A possible way to overcome
the effect of a priori knowledge of adverse neonatal outcome would be to introduce a blind evaluation of several
tracings, among which the index case is included. In clinical and research settings, case reviews involving CTG analysis should avoid the disclosure of neonatal outcome at the
start, and observations should not be limited to cases with
an adverse outcome.
The current study leaves many related questions unanswered. The impact of using other widely disseminated
CTG interpretation guidelines may not be similar, and
needs to be evaluated further. Adverse neonatal outcome
was defined in this study as umbilical artery acidaemia,
but would a knowledge of the more severe outcomes usually occurring in litigation cases provide similar results?
Do different levels of observer experience influence the
observed changes in classification? Finally, other areas of
obstetrics and gynaecology that have poorly reproducible
tests and frequent medical litigation may warrant similar
evaluations to assess whether analogous phenomena occur.
Disclosure of interest
All authors and their relations have no financial connections with companies that may have an interest in the submitted work, and no nonfinancial interests that may be
relevant to the article.
Contribution to authorship
Diogo Ayres-de-Campos had the original idea for the
study, proposed the initial version of the study design,
selected the cases, checked the results and wrote the first
version of the manuscript. Diana Arteiro contributed to
982
the study design, collected and transcribed clinicians’ analysis, evaluated the results and contributed to the manuscript
review. Cristina Costa-Santos contributed to the study
design, performed statistical analysis and contributed to the
manuscript review. João Bernardes provided several suggestions for study design and reviewed the final version of the
manuscript.
Details of ethics approval
Approval by the research ethics committees of the University Hospital Lund, University Hospital Malmo and
Sahlgrenska University Hospital, Gothenburg, was obtained
for the trial from which the tracings were taken,12 and all
participating women gave informed consent for use of
their data for research purposes. No person-identifiable
information was disclosed to clinicians in the present
study.
Funding
No external funding was obtained for this study. The
authors’ institutions sponsored the authors’ time dedicated
to the research.
Acknowledgements
The authors would like to thank Professor Sousa Barros
(Hospitais da Universidade de Coimbra), Dr Nuno Clode
(Hospital de Sta Maria, Lisbon), Doutora Filomena Nunes
(Hospital de Cascais), Dr Agostinho Carvalho (Hospital de
Viana do Castelo) and Dr Susana Pereira (Hospital de
Viseu) for analysing the tracings, and Dr Isis Amer-Wåhlin,
MD, PhD, and her co-authors from the Swedish randomised trial for allowing the use of their tracings.
Supporting information
The following supplementary materials are available for this
article:
Data S1. Powerpoint slides summarising the study.
Additional supporting information may be found in the
online version of this article.
Please note: Wiley-Blackwell are not responsible for the
content or functionality of any supporting information
supplied by the authors. Any queries (other than missing
material) should be directed to the corresponding
author. j
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Knowledge of neonatal outcome and CTG interpretation
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of fetal electrocardiogram for intrapartum fetal monitoring: a Swedish randomised controlled trial. Lancet 2001;358:534–8.
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Journal club
Discussion points
1. Background: Describe and compare National Institute for Health and Clinical Excellence (NICE),1 International
Federation of Gynaecology and Obstetrics (FIGO)2 and American College of Obstetrics and Gynecology (ACOG)3
guidelines for the interpretation of electronic fetal heart tracings.
2. Methods: Describe the study methods. Refer to the slides that accompany this BJOG article (Supporting Information
available online via bjog.org).
The tracings used in this study were taken with a STAN monitor in the second stage of labour. Discuss the
difference from usual practice in your unit. How could the results or their interpretation have been different if the
cardiotocographs (CTGs) had been obtained from the first stage of labour? Pay particular attention to Table 1.
Debate the use of umbilical artery pH < 7.05 as proxy for adverse outcome with reference to the essential and
nonspecific criteria of the cerebral palsy template.4 Reflect on the predictive value of pathological1,2 (abnormal3)
CTG tracings and low umbilical artery pH for cerebral palsy.
3. Results and implications: Discuss ways to improve the standardised interpretation of CTGs in practice5 or the analysis
of perinatal adverse events.6
Brainstorm possible techniques for the use of CTGs for educational or medicolegal purposes, avoiding a biased
interpretation. What would you do differently in your next CTG discussion meeting in the light of the findings
of this study? (Data S1) j
D Siassakos
University of Bristol and Southmead Hospital, Bristol, UK
Email [email protected]
ª 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology ª 2011 RCOG
983
Ayres-de-Campos et al.
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2 FIGO News: Rooth G, Huch A, Huch R. Guidelines for the use of fetal monitoring. Int J Gynecol Obstet 1987;25:159–67.
3 ACOG Practice Bulletin No. 106. Intrapartum fetal heart rate monitoring: nomenclature, interpretation, and general management principles.
Obstet Gynecol 2009;114:192–202.
4 MacLennan A. A template for defining a causal relation between acute intrapartum events and cerebral palsy: international consensus statement. Br Med J 1999;319:1054–9.
5 Draycott T, Sibanda T, Owen L, Akande V, Winter C, Reading S, et al. Does training in obstetric emergencies improve neonatal outcome?
BJOG 2006;113:177–82.
6 Kernaghan D, Penney GC. Do panels vary when assessing intrapartum adverse events? The reproducibility of assessments by hospital risk management groups Qual Saf Health Care 2006;15:359–62.
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ª 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology ª 2011 RCOG