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

Per Olofsson*

Department of Obstetrics and Gynecology, Malmo University Hospital, Lund University, S-205 02 Malmo, Sweden

Abstract

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 0.530.78) and for metabolic acidosis at birth 0.39

(0.210.72), in favor of the CTG ST method. CTG combined with ST analysis increases the ability of obstetricians to identify fetal hypoxiaand to intervene more appropriately, resulting in an improved perinatal outcome.

# 2003 Elsevier Ireland Ltd. All rights reserved.

Keywords: Cardiotocography; Electronic fetal monitoring; Fetal ECG; Pregnancy; ST analysis

1. Background

When electronic fetal heart rate monitoring, or cardiotoco-

graphy (CTG), was introduced 30 years ago, the aim was to

better identify fetuses affected by hypoxia during labor.

Subsequently, intrapartum death is nowadays a rare event

[1] and neonatal morbidity as manifested by seizures has

decreased [2]. However, many fetuses show heart rate changes

without being adversely affected and CTG has been criticized

to create an unnecessary high rate of operative deliveries

[1,3]. As a result, uncertainty surrounds CTG interpretation,

so that even pathological CTG patterns are misinterpreted

and newborns suffer hypoxic injury.

Experimental research has revealed that the fetal ECG

provides ST segment patterns related to the ability of the

fetal myocardium to respond to hypoxia [4,5]. An elevation

of the ST segment and the T wave amplitude, as quantified

by an increase of the T/QRS ratio, identifies a fetus that is

reacting to hypoxia by a catecholamine surge, beta-adreno-

ceptor activation, and myocardial glygogenolysis [68].

A T/QRS ratio increment indicates a fetus at risk of devel-

oping hypoxia but who is still capable of responding and

employ its defence against hypoxia. An ST segment depres-

sion, as identified by a biphasic or negative ST T segment,may indicate a situation when the myocardium cannot further

respond to hypoxia.

These experimental observations initiated the develop-

ment of a CTG ST waveform analyzer, the STAN1monitor [9,10]. In a randomized controlled trial, intrapartum

monitoring with CTG ST analysis (STAN1) resulted in a46% reduction of operative delivery for fetal distress

(ODFD) compared with CTG monitoring alone [11]. This

trial, known as the Plymouth RCT, also highlighted the need

for technical improvement of the ST analyzer to identify ST

segment depressions, and the importance of staff training.

Thus, a new STAN1 recorder was developed utilizing

novel digital signal processing capabilities and an automatic

assessment of the ST changes by means of an expert

systemthe ST event log [12]. After evaluation in observa-

tional clinical studies [12,13], the new system was validated

in the recently published Swedish multicenter RCT

(SwRCT) [14].

2. The Swedish randomized controlled trial onCTG + ST analysis versus CTG only monitoring

The aim of the SwRCT was to investigate the capability of

CTG ST analysis in labor to reduce both the number ofnewborns with metabolic acidosis and the number of ODFD,

as compared with monitoring with CTG alone.

The trial was conducted during 18 months at the uni-

versity departments in Gothenburg, Lund and Malmo. A

period of training and 2 months of using STAN1 S 21 fetal

heart monitor prototypes preceded the trial. Women in labor

European Journal of Obstetrics & Gynecology and

Reproductive Biology 110 (2003) S113S118

* Tel.: 46-40-331000; fax: 46-40-962600.E-mail address: per.olofsson@obst.mas.lu.se (P. Olofsson).

0301-2115/$ see front matter # 2003 Elsevier Ireland Ltd. All rights reserved.doi:10.1016/S0301-2115(03)00181-7

with singleton fetuses in vertex presentation at more than 36

completed gestational weeks were included after a decision

to apply a fetal scalp electrode. Internal monitoring was the

preferred method of surveillance in high-risk pregnancies,

cases of suspicious or abnormal external CTG, induced

or oxytocin-augmented labor, meconium-stained amniotic

fluid, or epidural analgesia. Allocation to monitoring with

either CTG (CTG group) or CTG ST analysis (CTG STgroup) was done at power-on of the monitor. No ECG

information was available in the CTG group.

Management in the CTG group was according to FIGO

guidelines [15] and in the CTG ST group it was guided bya CTG ST interpretation algorithm. Fetal scalp blood sam-pling (FBS) was optional at the discretion of the obstetrician

in both groups. Depending on the clinical circumstances,

suggested interventions were delivery, FBS, or alleviation

of a possible cause of fetal distress.

The major outcome measures were umbilical cord artery

metabolic acidosis (pH < 7:05 and base deficit in the extra-cellular fluid >12.0 mmol/L) and ODFD. In addition, the

neonatal morbidity was evaluated in terms of Apgar scores at

1 and 5 min and admission to the neonatal intensive care unit

(NICU). The rate of operative delivery for failure to progress

(ODFP) was also recorded. The trial protocol included an

interim analysis after enrolment of 1600 cases to assess the

incidence of metabolic acidosis.

Statistical analyses were performed strictly according

to intended-mode-of-surveillance, calculating the relative

risk (RR) with 95% confidence intervals (CI). The analyses

were performed at three levels: (1) all recruited cases

according to intention-to-treat (Table 1); (2) all eligible

cases according to the trial protocol (Table 2); (3) eligible

cases recruited after the interim analysis (Table 3).

A total of 4966 parturients were enrolled. The proportion

of recruited cases corresponded to 3136% of all deliveries.

Backround characteristics were similar in both groups,

although epidural analgesia was more common in the CTG

group (40%) compared with the CTG ST group (37%).The interim analysis revealed protocol violations in the

CTG ST group, because the staff were inclined to inter-vene according to the CTG patterns and neglect the STAN1

information. A new period of education, lectures, and feed-

back on cases managed locally was therefore commenced.

Five perinatal deaths occurred, two due to lethal mal-

formations and three related to intrapartum events. In all of

the latter three cases, the study protocol was violated. In one

case (CTG ST group) maternal fever occurred in labor andthe CTG showed a preterminal pattern without ST changes

(according to the CTG ST algorithm preterminal CTGpatterns should render immediate delivery irrespective of

ST waveforms). In one case (CTG ST group) both theCTG and the ST event log indicated fetal hypoxia, but this

was overlooked by the managing obstetrician and delivery

subsequently delayed. In the third case (CTG group) the

CTG pattern was abnormal, indicating severe hypoxia.

There were altogether 11 cases of hypoxic ischemic

encephalopathy (HIE) [16]. Of these, all the three cases

with neonatal seizures (HIE grade 2) occurred in the

Table 1

Outcome of the Swedish randomized controlled trial (SwRCT) on cardiotocography (CTG) ST analysis vs. CTG only: analysis according to intention-to-treat

CTG only: N 2447 (%) CTG ST: N 2519 (%) RR 95% CI P-valueODFD 9.3 7.7 0.83 0.690.99 0.047

ODFP 11.2 10.4 0.93 0.791.09 0.39

Apgar score

CTG group. There were no cases of intracerebral bleedings

(HIE grade 3).

The CTG ST group showed significantly lower rates ofmetabolic acidosis (0.7% versus 1.5%; RR 0.47, 95% CI

0.250.86) and ODFD (7.7% versus 9.3%; RR 0.83, 95% CI

0.690.99) than the CTG group when all cases were

included according to intention-to-treat [14]. The differ-

ences were more pronounced when only eligible cases were

considered, and further during the period after interim

analysis and re-training (Tables 13).

3. Neonatal outcome

The outcome of the 351 neonates admitted to the NICU in

the SwRCT were analyzed further in detail [20]. One baby

died and there were 28 other cases with an adverse/compli-

cated neonatal course. Of these, 22 had CTG ST patternsthat indicated a need for intervention according to the

CTG ST clinical guidelines. The number of livebornswith moderate or severe encephalopathy was significantly

lower in the CTG ST group (0.04%) compared with theCTG only group (0.33%). The odds ratio (OR) for adverse

and complicated outcomes is displayed in Table 4 in relation

to the level of statistical analysis. The results further support

the value of the STAN1method in labor to reduce the risk of

neonates being exposed to intrapartum hypoxia and the risk

to suffer brain damage.

4. Fetal scalp blood sampling or STAN1, or both?

In the SwRCT, FBS was performed in 10.7% in the CTG

group and in 9.3% in the CTG ST group (RR 0.87, 95% CI0.741.03; P 0:12) [14]. After the interim analysis and re-training, the corresponding figures were 11.8% versus 8.9%

(P 0:02). In six cases of FBS metabolic acidosis occurred:the FBS was abnormal in only one case (pH 7.13, ST events

then recorded for 80 min), whereas in the other five cases the

pH was normal (>7.20) and not repeated (Table 5). The ST

event log signaled abnormality existing for 25276 min in

five cases and in the sixth case the signal quality was

inadequate for ST analysis.

It is of concern at many delivery units starting to use the

STAN1 recorder how to use CTG ST in combination withFBS. FBS for pH determination was used in the SwRCT at

Table 3

Outcome of the SwRCT according to eligibility after interim analysis and re-training

CTG only: N 1049 (%) CTG ST: N 1054 (%) RR 95% CI P-valueODFD 8.7 5.0 0.56 0.390.80 0.001

ODFP 11.0 11.6 1.06 0.901.41 0.71

Apgar score

the discretion of the managing obstetrician, and the aim was

not to include an assessment of the clinical value and

reliability of FBS. Only future RCTs can resolve the ques-

tion which method is the most reliable and the question

whether CTG ST can replace FBS. At present, there areno answers based on scientific results. Due to the low

incidence of metabolic acidosis at birth it can be predicted

that extraordinary efforts will be needed to perform such a

study. Meanwhile, only opinions based on observational

data are available.

In Table 5, a compilation of data from a Nordic observa-

tional study [21], the SwRCT [14], and from the European

Union (EU) project on fetal ECG in labor [17] is presented.

Altogether, the series comprises 9508 cases. Metabolic

acidosis occurred in 89 cases (0.94%). Of these 89 cases,

significant ST events were reported automatically by the ST

log in 73 cases (82.0%), but FBS was performed in only 15

cases (16.9%). Furthermore, FBS indicated fetal acidosis in

only six of these 15 cases; ST events were present for a

period of 280 min in all of these six cases.

This compilation (Table 5) shows that FBS was performed

in only a small proportion of cases with metabolic acidosis

but the ST event log frequently presented information on

significant ST events, suggesting a risk of fetal hypoxia.

Since the STAN1 method provides continuous on-line

information about fetal status, but the FBS procedure is

relatively arduous to perform and only presents momentary

information, it is possible that STAN1will outmode FBS for

practical reasons. The FBS procedure is more time-consum-

ing than the STAN1method and carries a risk of delaying an

urgent intervention. However, at delivery units presently

using FBS for pH or lactate determinations in fetal scalp

blood it seems wise to sustain these methods until further

experience is gained.

5. Current status of CTG + ST analysis in Europe

At the present time (September 2001), two observation

studies [12,21] and two RCTs [11,14] on the clinical use of

CTG ST monitoring in labor have been conducted. Inaddition, the STAN1 concept is used at 10 European uni-

versity clinics, certified as centers of excellence (CoE).

These CoE, in Berlin, Copenhagen, Derby, Gothenburg,

Lyon, Oslo, Perugia, Plymouth, Turkku and Utrecht, are

economically supported by the European Union. The aim of

the EU project is to secure a safe use of the STAN1

technology, by which new STAN1 users are provided with

educational material and participate in regional workshops.

They are further supported by the regional CoE to become

certified users.

The current status of CTG ST analysis in Europe issummarized in Table 6. Still, a majority of ODFD at the ten

CoE is performed on other indications than CTG STchanges. The increase of both metabolic acidocis and

adverse outcomes is explained by a more selective use of

the STAN1method in high-risk pregnancies. The combined

incidence of perinatal mortality and moderate/severe HIE

in the SwRCT [14] and the EU project [17] was 0.61/1000

in the CTG ST group and 4.2/1000 in the CTG group(OR 0.15; 95% CI 0.040.48; P < 0:001).

Two RCTs on CTG only versus CTG ST analysis inlabor have now been performed in Europe [11,14]. Alto-

gether, more than 6800 cases have been included (Table 7).

Overall, intrapartum CTG ST monitoring shows a 35%reduction of ODFD and a 61% reduction of metabolic

acidosis at birth.

6. The need for education, training andmotivation of staff members

In the SwRCT, the reduction of metabolic acidosis obtained

in the CTG ST group was 53% when all recruited caseswere included (Table 1), but after exclusion of cases with

inadequate monitorings the rate increased to 60% (Table 2).

Table 6

Development and current status (September 2001) of the European Union

project on intrapartum fetal ECG monitoring (N 3969)First 2161 cases (%) Next 1808 cases (%)

ODFD 17.6a 14.1b

Metabolic acidosis 0.7 1.2

Adverse neonatal outcomec 0.2 0.7

a 7% on ST event indication.b 6% on ST event indication.c Including cases of HIE and metabolic acidosis at birth necessitating

transfer to the NICU.

Table 7

Combined results of the Plymouth RCT [11] and SwRCT [14] on fetal ECG ST waveform analysis in labor

Plymouth: N 2434 (%) Swedish: N 4392 (%)a Combined: N 6826 (%) OR 95% CI P-valueODFD

CTG 9.1 8.0 8.4

CTG ST 5.0 5.9 5.6 0.65 0.530.78

The difference became more pronounced after the interim

analysis and re-training period, whereupon the figure

increased to 72% (Table 3). The corresponding figures for

ODFD were 17, 26 and 44, respectively. These figures

highlight the importance of staff training, feed-back, and

motivation when introducing a new technology. In the

SwRCT, we experienced that after the results of the interim

analysis had been presented to the staff and cases from the

own local delivery unit scrutinized and discussed, the moti-

vation to use the STAN1 recorder and follow the clinical

guidelines increased and the method was accepted. The

dissemination of new and advanced technology in the field

of perinatal medicine is a delicate task, which, surprisingly,

is not yet regulated by any governmental authorities.

7. Discussion

The Swedish multicenter RCT demonstrated that moni-

toring term fetus with CTG combined with ST analysis

(STAN1) during labor led to a significant improvement

of perinatal outcome. This is the first study to show a new

fetal monitoring methodology capable of reducing both

the risk of fetal exposure to severe intrapartum hypoxia

and the number of operative deliveries for fetal distress.

Thereby achieving what has recently been required from

new development in electronic fetal monitoring [18].

These findings confirm the results from experimental

research, that STwaveform analysis of the fetal ECG reflects

significant fetal hypoxia [46]. They also confirm the

Plymouth study findings, that addition of ST analysis to

conventional CTG improves the specificity of intrapartum

monitoring by reducing the rate of operative deliveries for

fetal distress [11]. Moreover, there was no increase of opera-

tive deliveries for other indications in any of these studies, as

the case was in a RCT on intrapartum fetal pulse oximetry

monitoring [19].

The most important finding in the Swedish RCT was the

significant reduction of metabolic acidosis at birth, being

1.5% in the CTG group and 0.7% in the CTG ST group. STanalysis seems of value in the prevention of intrapartum

asphyxia also in settings with a rather low incidence of this

complication. This conclusion is further supported by the

trends of fewer cases of adverse/complicated neonatal

outcome and neonatal encephalopathy in the CTG STgroup.

The STAN1 recorder performs the fetal ECG analysis

automatically, but the method still requires the CTG to be

interpreted by the clinician, as illustrated by some cases of

perinatal death. Naturally, intervention must also be based

on the stage of labor and additional clinical information.

More experience is needed about fetal ECG changes in

specific groups, e.g. fetuses with intrauterine infection,

growth restriction, diabetes, and preterm fetuses.

The STAN1 method is not only a new recorder, but

a concept comprising a technical equipment, automatic

interpretation, and educational material. The STAN1 con-

cept includes advanced technology with an expert system,

the ST event log, that automatically provides the user with

information about significant ECG changes. The training

program includes educational material covering basic

fetal physiology and pathophysiology, CTG interpretation,

ST interpretation, assessment of the newborn, both in

booklet form and in a multimedia-based format (CD) for

self-training.

After publication of the Swedish RCT last year [14], the

STAN1method has attracted much interest and gained wide

acceptance. There are good reasons to claim the method will

come up to anticipations.

Acknowledgements

The members of the Swedish STAN1 study group are

gratefully acknowledged: Dr. Isis Amer-Wahlin, Dr. Char-

lotte Hellsten, Dr. Henrik Hagberg, Dr. Andreas Herbst,

Dr. Ingemar Kjellmer, Dr. Hakan Lilja, Dr. Claes Lindoff,

Dr. Karel Marsal, Ms. Majvi Mansson, R.N., Ms. Laila

Martensson, R.N., Dr. Hakan Noren, Dr. Per Olofsson,

and Ms. Anna-Karin Sundstrom, R.N. For providing data

from the European Union project, Dr. Karl G. Rosen, Ms.

Anna-Karin Sundstrom, R.N., and Ms. Ulla-Stina Wilson,

R.N., are gratefully acknowledged.

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