British Journal of Obstetrics and Gynaecology January 1992, Vol. 99, pp. 32-37
FETAL AND NEONATAL M E D I C I N E
Clinical assessment of fetal electrocardiogram monitoring in labour K A R L W. M U R P H Y VIRGINIA RUSSELL PAUL JOHNSON Nuffield Department of Obstetrics and G ynaecology John Radcliffe Hospital, Maternity Department, Headington, Oxford OX3 9DU, UK J A N E VALENTE Department of Gynaecology, Churchill Hospital, Oxford OX3 7LJ, UK
ABSTRACT Objective To assess the potential clinical value of fetal electrocardiographic (ECG) monitoring in labour. Design Descriptive study of the use of ECG waveform analysis during labour and its correlation with other indices of fetal and neonatal well-being. Setting Teaching hospital in Oxford. Subjects 86 high risk pregnancies. Main outcome measures Suitability of ST Segment Analyser (Cinventa, Sweden) for clinical use; relation between the T/QRS ratio during labour (an index of ST segment and T wave elevation) and intrapartum cardiotocography, umbilical artery pH at birth and Apgar scores; T/QRS ratio trends in labour. Results The system was robust and user-friendly. No statistically significant relation was found between T/QRS ratios in labour and FHR abnormalities in the cardiotocograph. There was a weak relation between T/QRS ratios and umbilical artery acidosis: at a cervical dilatation of 4 cm, the Spearman rank correlation of the mean T/QRS ratio with umbilical artery actual base deficit was I' = -0.31, 0.05 >P>O.O 1. The correlation of T/QRS with the umbilical artery pH was not statistically significant, although a trend was present (Spearman rank: I' = -0.26, P>O.OS). Correlation of the T/QRS ratio with Apgar scores at 1 and at 5 min was not statistically significant. Only 3 of 16 infants with an Apgar score of < 7 at 1 min had a mean T/QRS ratio above 0.25 at any time during labour. Conclusions Further research is necessary before a decision can be made whether this new method of fetal monitoring should be introduced into clinical practice.
The deficiencies of electronic FHR (fetal heart rate) monitoring in labour are well recognised (Sykes et al. 1983) and there is an urgent need to find better methods of intrapartum fetal surveillance (Sawers 1983). It has been suggested that continuous monitoring of the waveform of the fetal electrocardiogram (ECG) in labour may be a useful method for detecting fetal hypoxia and acidosis (Jenkins et al. 1986). Many of the technical problems associated with automated measurements of the fetal ECG waveform have been overcome in recent years. Various systems based on computer averaging have been developed to improve the signal-to-noise ratio. One such system is the ST segment analyser (STAN). The STAN was constructed in Gothenburg, Sweden, based on evidence from animal studies that the main response to fetal hypoxaemia was a progressive increase in the amplitude of the T wave, together with elevation of the ST segment (Rosen & Kjellmer 197.5). Work by Hokegard et al. (1 979) and Greene et al. ( I 982) showed that ST waveform elevation occurred when fetal hypoxia led to anaerobic myocardial metabolism. Changes in the ST segment and T wave are known to appear in advance of cardiovascular failure (Rosen et al. 1976). EssenCorrespondence: Dr Karl Murphy, Senior Registrar & Fellow in Fetal Medicine, Department of Obstetrics and Gynaecology, The Queen Mother's Hospital, Yorkhill, Glasgow G3 8SH, UK.
32
tially, the STAN produces a continuous read-out of the ratio between the amplitude of the T wave and the amplitude of the QRS complex (T/QRS ratio), together with intermittent plots of the computer-averaged fetal ECG waveform, throughout labour. The aim of this descriptive study was to investigate the potential of ST waveform monitoring in labour as a clinical tool. ST waveform changes were correlated with changes in the intrapartum cardiotocogram (CTG) and with indices of the infant's condition at birth: Apgar scores and umbilical cord acid-base measurements.
Subjects and methods Fetal ECG recordings were obtained from 86 women who had continuous electronic fetal heart rate monitoring during labour. In this hospital 50% of all women required intrapartum electronic monitoring during the study period and it was from this group that subjects were recruited into the study. Availability of the equipment and research staff determined whether any woman from this group would be asked to participate. The major indications for fetal monitoring in the study group were as follows: ( 1) antepartum: hypertension/intrauterine growth retardation 28%, prolonged pregnancy 13%, previous cae-
FIELD ECG M O N I T O R I N G I N L A B O U R
sarean section 6%, miscellaneous 9%; (2) intrapartum: in 24% monitoring was started during labour because oxytocin or epidural analgesia were used. Meconium staining of the amniotic fluid was the indication for monitoring in a further 16%. Fetal distress diagnosed by auscultation was the indication in 4%. Table 1 shows the obstetric characteristics of the study population. Fifty eight (67%) were nulliparous. The mean age was 26 (range 18-34). There was a high frequency of induction of labour, epidural anaesthesia and instrumental and operative deliveries. Fetal outcome was assessed by Apgar scores, cord blood acid-base measurements at delivery (using Radiometer ABL3 blood gas analyser) and the need for admission to the neonatal special care unit. Apgar scores were recorded for all the babies. The pH, Po,, Pco, and base deficit were determined in blood from the umbilical artery and the vein for 97% of the babies. The ‘actual’ base deficit was estimated: this is a measure of the metabolic component of the acidosis that is not corrected for Pco2 level. The base deficit in the extracellular fluid was also calculated using the Siggaard-Andersen acidbase chart (1971) and this is more representative of the true metabolic component of the acidosis. Umbilical artery acidosis, pH
FETAL AND NEONATAL M E D I C I N E
Clinical assessment of fetal electrocardiogram monitoring in labour K A R L W. M U R P H Y VIRGINIA RUSSELL PAUL JOHNSON Nuffield Department of Obstetrics and G ynaecology John Radcliffe Hospital, Maternity Department, Headington, Oxford OX3 9DU, UK J A N E VALENTE Department of Gynaecology, Churchill Hospital, Oxford OX3 7LJ, UK
ABSTRACT Objective To assess the potential clinical value of fetal electrocardiographic (ECG) monitoring in labour. Design Descriptive study of the use of ECG waveform analysis during labour and its correlation with other indices of fetal and neonatal well-being. Setting Teaching hospital in Oxford. Subjects 86 high risk pregnancies. Main outcome measures Suitability of ST Segment Analyser (Cinventa, Sweden) for clinical use; relation between the T/QRS ratio during labour (an index of ST segment and T wave elevation) and intrapartum cardiotocography, umbilical artery pH at birth and Apgar scores; T/QRS ratio trends in labour. Results The system was robust and user-friendly. No statistically significant relation was found between T/QRS ratios in labour and FHR abnormalities in the cardiotocograph. There was a weak relation between T/QRS ratios and umbilical artery acidosis: at a cervical dilatation of 4 cm, the Spearman rank correlation of the mean T/QRS ratio with umbilical artery actual base deficit was I' = -0.31, 0.05 >P>O.O 1. The correlation of T/QRS with the umbilical artery pH was not statistically significant, although a trend was present (Spearman rank: I' = -0.26, P>O.OS). Correlation of the T/QRS ratio with Apgar scores at 1 and at 5 min was not statistically significant. Only 3 of 16 infants with an Apgar score of < 7 at 1 min had a mean T/QRS ratio above 0.25 at any time during labour. Conclusions Further research is necessary before a decision can be made whether this new method of fetal monitoring should be introduced into clinical practice.
The deficiencies of electronic FHR (fetal heart rate) monitoring in labour are well recognised (Sykes et al. 1983) and there is an urgent need to find better methods of intrapartum fetal surveillance (Sawers 1983). It has been suggested that continuous monitoring of the waveform of the fetal electrocardiogram (ECG) in labour may be a useful method for detecting fetal hypoxia and acidosis (Jenkins et al. 1986). Many of the technical problems associated with automated measurements of the fetal ECG waveform have been overcome in recent years. Various systems based on computer averaging have been developed to improve the signal-to-noise ratio. One such system is the ST segment analyser (STAN). The STAN was constructed in Gothenburg, Sweden, based on evidence from animal studies that the main response to fetal hypoxaemia was a progressive increase in the amplitude of the T wave, together with elevation of the ST segment (Rosen & Kjellmer 197.5). Work by Hokegard et al. (1 979) and Greene et al. ( I 982) showed that ST waveform elevation occurred when fetal hypoxia led to anaerobic myocardial metabolism. Changes in the ST segment and T wave are known to appear in advance of cardiovascular failure (Rosen et al. 1976). EssenCorrespondence: Dr Karl Murphy, Senior Registrar & Fellow in Fetal Medicine, Department of Obstetrics and Gynaecology, The Queen Mother's Hospital, Yorkhill, Glasgow G3 8SH, UK.
32
tially, the STAN produces a continuous read-out of the ratio between the amplitude of the T wave and the amplitude of the QRS complex (T/QRS ratio), together with intermittent plots of the computer-averaged fetal ECG waveform, throughout labour. The aim of this descriptive study was to investigate the potential of ST waveform monitoring in labour as a clinical tool. ST waveform changes were correlated with changes in the intrapartum cardiotocogram (CTG) and with indices of the infant's condition at birth: Apgar scores and umbilical cord acid-base measurements.
Subjects and methods Fetal ECG recordings were obtained from 86 women who had continuous electronic fetal heart rate monitoring during labour. In this hospital 50% of all women required intrapartum electronic monitoring during the study period and it was from this group that subjects were recruited into the study. Availability of the equipment and research staff determined whether any woman from this group would be asked to participate. The major indications for fetal monitoring in the study group were as follows: ( 1) antepartum: hypertension/intrauterine growth retardation 28%, prolonged pregnancy 13%, previous cae-
FIELD ECG M O N I T O R I N G I N L A B O U R
sarean section 6%, miscellaneous 9%; (2) intrapartum: in 24% monitoring was started during labour because oxytocin or epidural analgesia were used. Meconium staining of the amniotic fluid was the indication for monitoring in a further 16%. Fetal distress diagnosed by auscultation was the indication in 4%. Table 1 shows the obstetric characteristics of the study population. Fifty eight (67%) were nulliparous. The mean age was 26 (range 18-34). There was a high frequency of induction of labour, epidural anaesthesia and instrumental and operative deliveries. Fetal outcome was assessed by Apgar scores, cord blood acid-base measurements at delivery (using Radiometer ABL3 blood gas analyser) and the need for admission to the neonatal special care unit. Apgar scores were recorded for all the babies. The pH, Po,, Pco, and base deficit were determined in blood from the umbilical artery and the vein for 97% of the babies. The ‘actual’ base deficit was estimated: this is a measure of the metabolic component of the acidosis that is not corrected for Pco2 level. The base deficit in the extracellular fluid was also calculated using the Siggaard-Andersen acidbase chart (1971) and this is more representative of the true metabolic component of the acidosis. Umbilical artery acidosis, pH
