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Fetal electrocardiogram (ECG) for fetal monitoring during
labour (Review)
Neilson JP
ThisisareprintofaCochranereview,preparedandmaintained byTheCochraneCollaborationandpublishedinTheCochraneLibrary
2007, Issue 2
http://www.thecochranelibrary.com
Fetal electrocardiogram (ECG) for fetal monitoring during labour (Review) 1
Copyright©2007 The CochraneCollaboration.Published byJohn Wiley & Sons, Ltd
TABLE OF CONTENTS
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
PLAINLANGUAGESUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
CRITERIAFORCONSIDERINGSTUDIESFORTHISREVIEW . . . . . . . . . . . . . . . . . . 3
SEARCHMETHODSFORIDENTIFICATIONOFSTUDIES . . . . . . . . . . . . . . . . . . . 3
METHODSOFTHEREVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
DESCRIPTIONOFSTUDIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
METHODOLOGICALQUALITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
AUTHORS’CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
POTENTIALCONFLICTOFINTEREST . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
SOURCESOFSUPPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Characteristics of included studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Characteristics of excluded studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Characteristics of ongoing studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
ANALYSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Comparison 01. Fetal ECG plus CTG versus CTG alone . . . . . . . . . . . . . . . . . . . . . 9
INDEXTERMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
COVERSHEET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
GRAPHSANDOTHERTABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Analysis 01.01. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 01 Perinatal death . . . . . 11
Analysis 01.02. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 02 Neonatal encephalopathy . . 12
Analysis 01.04. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 04 Apgar score < 7 at 5 minutes . 13
Analysis 01.05. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 05 Cord pH < 7.05 + base deficit > 14
12 mmol/L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analysis 01.06. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 06 Cord artery pH < 7.05 . . . 15
Analysis 01.07. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 07 Cord artery pH < 7.15 . . . 16
Analysis 01.08. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 08 Neonatal intubation . . . 17
Analysis 01.09. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 09 Admission neonatal special care 18
unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analysis 01.10. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 10 Caesarean section . . . . 19
Analysis 01.11. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 11 Operative vaginal delivery . 20
Analysis 01.12. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 12 All operative deliveries . . . 21
Analysis 01.13. Comparison 01 Fetal ECG plus CTG versus CTG alone, Outcome 13 Fetal blood sampling . . . 22
Fetal electrocardiogram (ECG) for fetal monitoring during labour (Review) i
Copyright©2007 The CochraneCollaboration.Published byJohn Wiley & Sons, Ltd
Fetal electrocardiogram (ECG) for fetal monitoring during
labour (Review)
Neilson JP
This record should be cited as:
Neilson JP. Fetal electrocardiogram (ECG) for fetal monitoring during labour. Cochrane Database of Systematic Reviews 2006, Issue 3.
Art. No.: CD000116. DOI: 10.1002/14651858.CD000116.pub2.
This version first published online: 19 July 2006 in Issue 3, 2006.
Date of most recent substantive amendment: 06 April 2006
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
ECGduring 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 strategy
WesearchedtheCochrane Pregnancy and Childbirth Group’s Trials Register (April 2006).
Selection criteria
Randomised trials comparing fetal ECG waveform analysis with alternative methods of fetal monitoring during labour.
Data collection and analysis
Trial quality assessment and data extraction were performed by the review author, without blinding.
Main results
Four trials including a total of 9829 women were included. In comparison to continuous electronic fetal heart rate monitoring alone,
the use of adjunctive ST waveform analysis (three trials, 8872 women) was associated with fewer babies with severe metabolic acidosis
at birth (cord pH less than 7.05 and base deficit greater than 12 mmol/L) (relative risk (RR) 0.64, 95% confidence interval (CI) 0.41
to 1.00, data from 8108 babies), fewer babies with neonatal encephalopathy (three trials, RR 0.33, 95% CI 0.11 to 0.95) although
the absolute number of babies with encephalopathy was low (n = 17), fewer fetal scalp samples during labour (three trials, RR 0.76,
95% CI 0.67 to 0.86) and fewer operative vaginal deliveries (three trials, RR 0.87, 95% CI 0.78 to 0.96). There was no statistically
significant difference in caesarean section (three trials, RR 0.97, 95% CI 0.84 to 1.11), Apgar score less than seven at five minutes
(three trials, RR 0.80, 95% CI 0.56 to 1.14), or admissions to special care unit (three trials, RR 0.90, 95% CI 0.75 to 1.08). Apart
fromatrend towards feweroperative deliveries (one trial, RR 0.87, 95% CI 0.76 to 1.01), there was little evidence that monitoring by
PRinterval analysis conveyed any benefit.
Authors’ conclusions
ThesefindingsprovidesomesupportfortheuseoffetalSTwaveformanalysiswhenadecisionhasbeenmadetoundertakecontinuous
electronic fetal heart rate monitoring during labour. However, the advantages need to be considered along with the disadvantages of
needing to use an internal scalp electrode, after membrane rupture, for ECG waveform recordings.
Fetal electrocardiogram (ECG) for fetal monitoring during labour (Review) 1
Copyright©2007 The CochraneCollaboration.Published byJohn Wiley & Sons, Ltd
PLAIN LANGUAGE SUMMARY
Monitoring the baby’s heart using electrocardiography (ECG) plus cardiotocography (CTG) during labour helps mothers and babies
whencontinuous monitoring is needed
Electronic heart monitoring may be suggested if doctors think the baby is not getting enough oxygen during labour. Two methods may
be used. CTG measures the baby’s heart rate. ECG measures the heart’s electrical activity and the pattern of the heart beats. ECG uses
anelectrode,passed through thewoman’s cervix, and attached to the baby’s head. The review of trials found that using ECG plus CTG
results in fewer blood samples taken from the baby’s scalp, less surgical assistance and better oxygen levels at birth than CTG alone.
BACKGROUND ischaemic encephalopathy due to hypoxaemic brain damage and
may be linked to subsequent neuro-developmental disability, in-
Labour poses a potential threat to fetal wellbeing. The supply of cluding cerebral palsy. It should therefore be an important goal of
oxygen to the fetus requires an adequate supply of maternal blood obstetric care to avoid neonatal convulsions. However, it is also
to the placenta, a properly functioning placenta to allow transfer important to avoid unnecessary obstetric intervention.
of oxygen from maternal to fetal blood, and a patent umbilical Cardiotocographic traces maybedifficulttointerpret,resultingin
vein in the umbilical cord to the fetus. Strong uterine contractions unnecessaryoperativeintervention,whilesomesignificantchanges
in labour stop the flow of maternal blood to the placenta with go unrecognised (Ennis 1990). Computerised cardiotocography
intermittentdecreasesinoxygenation.Mostfetuseshavesufficient has not proved helpful during labour (Dawes 1994). However,
metabolic reserve to withstand this effect but those with limited there is some evidence that fetal blood sampling, as an adjunc-
reserves, notably malnourished ’growth restricted’ fetuses, may tive test along with cardiotocography, may decrease unnecessary
become distressed. The umbilical cord may also be compressed intervention without jeopardising fetal outcome. No clinical tri-
during labour, especially if the membranes are ruptured, which als have directly compared fetal monitoring by cardiotocography
mayalso cause distress. alone versus cardiotocography with the option of fetal scalp sam-
The earliest method of monitoring fetal wellbeing during labour pling. However,trials comparing cardiotocography withintermit-
wasbyusingthefetal(Pinard)stethoscopeintermittentlytocalcu- tent auscultation show a greater increase in caesarean section rates
latethefetalheartrate.Duringthe1960sand1970s,electronicsys- when fetal scalp sampling was not available (RR 1.79, 95% CI
temsweredevelopedtoallowmonitoringofthefetalheartrateto- 1.41 to 2.27) than when available (RR 1.26, 95% CI 1.05 to
gether with the mother’s uterine contractions (cardiotocography), 1.51) (Alfirevic 2006). Scalp sampling is an awkward, uncomfort-
and these have been very widely used. To monitor the heart rate, able procedure for the mother and involves a stab incision in the
signals can be obtained from an ultrasound transducer strapped to scalp of the fetus. This has limited its appeal (Clark 1985; Wheble
themother’sabdomen,orfromanelectrodeclippedintothebaby’s 1989) and pre-empts its use in areas with a high prevalence of
scalp. Traces of the baby’s heart rate may be ’continuous’ (that is, HIVinfection.Anadditionaldrawbackisthat,byitsnature,scalp
throughoutlabour)orintermittent.Althoughthemother’smobil- sampling can only give intermittent information about fetal acid-
ity is limited by both methods, this is obviously greater with con- base status.
tinuous monitoring. Non-reassuring features on a cardiotocogra- Toaddress thesechallengesin intrapartum fetal monitoring, tech-
phytracewouldincludeunusuallyrapidorslowrates,aflatpattern nology has been developed to monitor the fetal electrocardio-
(reduced variability), and certain types of heart rate decelerations graphic (ECG) waveform during labour. If shown helpful to ei-
(especially ’late’ or ’severe variable’ decelerations). Such observa- ther improvefetal outcome, or decrease unnecessary intervention,
tions might prompt further intervention in the form of operative or both, this has the potential advantage of providing continuous
delivery, or additional testing of fetal condition (see below). information as well as being less invasive than fetal scalp sampling
A systematic review of randomised trials comparing continuous (although it is not non-invasive: requiring a signal obtained from
electronic fetal heart rate monitoring (cardiotocography) and in- an electrode embedded in the fetal scalp).
termittent auscultation (Alfirevic 2006) showed fewer babies hav- ThefetalECG,liketheadultECG,displaysP,QRS,andTwaves
ing neonatal convulsions after continuous monitoring (relative corresponding to electrical events in the heart during each beat.
risk (RR) 0.50, 95% confidence interval (CI) 0.31 to 0.80) but The P wave represents atrial contraction, QRS ventricular con-
at the cost of increased rates of obstetric intervention in the form traction, and T ventricular repolarisation. Two parts of the fetal
of caesarean section (RR 1.66, 95% CI 1.30 to 2.13) and instru- ECGwaveformhaveattractedattention fromresearchers:PR/RR
mental vaginal delivery (RR 1.16, 95% CI 1.01 to 1.32). Neona- relations and the ST waveform (Greene 1999). Normally there is
tal convulsions are often, but not always, associated with hypoxic- a positive correlation between the PR interval (the time between
Fetal electrocardiogram (ECG) for fetal monitoring during labour (Review) 2
Copyright©2007 The CochraneCollaboration.Published byJohn Wiley & Sons, Ltd
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