Variation in the T/QRS ratio of fetal electrocardiograms recorded during labour in normal subjects

The T/QRS ratio of the fetal ECG was obtained during labour from 25 women with normal pregnancies. The poor signal-to-noise ratio of the unprocessed signals, chiefly due to baseline wander, led to a wide variation between individual measurements. This problem was overcome by data averaging, the ratio being expressed as a mean over 1-min epochs. The average T/QRS ratio of each labour record ranged from 4% to 23% with a mean of 10% (for all 25). The average range (between 5th and 95th centile) of the 1-min T/QRS ratios was 13% and there were no significant changes as labour progressed. The effect of contractions on the T/QRS ratio was measured from eight subjects and found to be inconsistent.     

Variation in the T/QRS ratio of fetal electrocardiograms recorded during labour in normal subjects

Summary. The T/QRS ratio of the fetal ECG was obtained during labour from 25 women with normal pregnancies. The poor signal-to-noise ratio of the unprocessed signals, chiefly due to baseline wander, led to a wide variation between individual measurements. This problem was overcome by data averaging, the ratio being expressed as a mean over 1-min epochs. The average T/QRS ratio of each labour record ranged from 4% to 23% with a mean of 10% (for all 25). The average range (between 5th and 95th centile) of the 1-min T/QRS ratios was 13% and there were no significant changes as labour progressed. The effect of contractions on the T/QRS ratio was measured from eight subjects and found to be inconsistent.     

Fetal ECG waveform analysis should improve fetal surveillance in labour

Fetal heart rate (FHR) and fetal electrocardiogram (ECG) recordings were obtained from a scalp electrode with maternal thigh as reference and used for ST waveform analysis in 201 patients in labour. Nearly 45% had suspicious or abnormal FHR traces whilst only 27% had T/QRS ratio greater than 0.25 (mean +/- 2 SD). A normal T/QRS ratio identified 99.3% of fetuses with normal buffering capacity in cord artery blood. Of 13 infants with a cord artery blood pH less than 7.15, standard bicarbonate was less than 15.0 mmol/l in five who had an average T/QRS ratio less than 0.25 throughout labour. Of the eight with respiratory acidosis, five had an increase in T/QRS ratio greater than 0.25 for longer than 20 minutes prior to delivery, in two the ratio increased during the last few minutes and one had no change (pH 7.14). Persistent elevation of T/QRS in the first stage of labour identified those with decrease in buffer capacity in cord arterial blood (sensitivity of 94.1%). Acute hypoxia was recognized by the rapid rise in T/QRS. The specificity of T/QRS to identify fetuses at risk increased by combining the ST waveform analysis with FHR changes.     

Comparison of the T/QRS ratio of the fetal electrocardiogram and the fetal heart rate during labour and the relation of these variables to condition at delivery

Summary. The T/QRS ratio of the fetal electrocardiogram (ECG) was recorded to within 30 min of delivery from 105 women in labour. There were no significant differences in the mean T/QRS ratio in the last hour of record between those with normal and intermediate, or abnormal fetal heart rate (FHR) patterns. In 66 labours the mean T/QRS ratio in the first hour of record was compared with that of the last hour; the only significant change was a small decrease in the mean ratio from 11% to 7% in a group of 11 fetuses with an abnormal FHR pattern throughout the recording time. Eight babies were born with evidence of acidosis (umbilical artery pH<7.16), and another four were born in poor condition (1 min Apgar score <4) without evidence of acidosis; none had a mean last hour T/QRS ratio significantly different from the previously established normal range.     

Comparison of the T/QRS ratio of the fetal electrocardiogram and the fetal heart rate during labour and the relation of these variables to condition at delivery

The T/QRS ratio of the fetal electrocardiogram (ECG) was recorded to within 30 min of delivery from 105 women in labour. There were no significant differences in the mean T/QRS ratio in the last hour of record between those with normal and intermediate, or abnormal fetal heart rate (FHR) patterns. In 66 labours the mean T/QRS ratio in the first hour of record was compared with that of the last hour; the only significant change was a small decrease in the mean ratio from 11% to 7% in a group of 11 fetuses with an abnormal FHR pattern throughout the recording time. Eight babies were born with evidence of acidosis (umbilical artery pH less than or equal to 7.16), and another four were born in poor condition (1 min Apgar score less than 4) without evidence of acidosis; none had a mean last hour T/QRS ratio significantly different from the previously established normal range.     

The effect of fetal head compression and fetal acidaemia during labour on human fetal cerebral function as measured by the fetal electroencephalogram.

We investigated the effect of head compression and acidaemia during labour in 25 African primigravidae. Evidence that head compression had occurred during labour was confirmed by both clinical and radiological means at the end of a trial of labour. No significant difference could be demonstrated in the quantity of fetal electroencephalogram (EEG) abnormality that occurred in the groups with marked head compression as compared to the groups without marked head compression. Deterioration in the fetal EEG to a flat record known as electrocerebral silence (ECS) was associated with the development of acidaemia. As fetal heart rate (FHR) decelerations appeared the percentage of ECS in the fetal EEG record increased significantly (P less than 0.05), and likewise, as fetal acidaemia developed a highly significant increase in ECS in the fetal EEG was demonstrated (P less than 0.001). We concluded that in the management of trial of labour there was no significant deleterious change in the fetal EEG as a result of head compression, unless fetal acidaemia supervened. However, in the majority of these cases a significant increase in ECS to more than 20 per cent occurred in association with only moderate acidaemia (pH 7.25 to 7.30).     

Maternal fever in term labour in relation to fetal tachycardia, cord artery acidaemia and neonatal infection

Objective To determine 1. whether maternal fever during term labour is associated with acidaemia at birth and neonatal infection and 2. whether fetal tachycardia precedes maternal fever and is associated with neonatal infection.
Design Retrospective matched-pair case-control study.
Subjects Two hundred and forty-eight newborn infants whose mothers developed fever during term labour (cases) and 248 control infants. The women were matched for parity and duration of labour.
Main outcome measures Cord artery acid-base status, Apgar scores, neonatal infections, and fetal heart rate before maternal fever.
Results Mean pH, as well as the rate of cord artery acidaemia at birth (pH < 7.10) was equal in cases and controls (in both groups 7.24% and 6%, respectively). Signs of septicaemia and/or pneumonia were identified in 17 case newborns (7%) and in one control (0.4%; OR 17.0,   P < 0.001  ). Of 212 pairs with complete heart rate data, fetal tachycardia preceded maternal fever in 39 cases (18%) and in 16 controls (8%) (OR 2.6,   P = 0.003  ). Tachycardia before maternal fever was not associated with increased neonatal infectious morbidity.
Conclusions Maternal fever during term labour was associated with perinatal infection, but not with acidaemia at birth. Elevated fetal heart rate preceded maternal fever in a minority of cases and was not associated with perinatal infection.     

Fetal heart rate patterns and ECG ST segment changes preceding metabolic acidaemia at birth

OBJECTIVES: To compare the rates of abnormal ST segment patterns of the ECG and cardiotocographic (CTG) abnormalities in fetuses with metabolic acidaemia at birth and controls. To evaluate the inter-observer agreement in interpretation of ST analysis and CTG. DESIGN: Case-control study. SETTING: Three University hospitals in southern Sweden. POPULATION: Cases and controls were selected from the Swedish randomised controlled trial on intrapartum monitoring, including 4966 fetuses monitored with a scalp electrode. METHODS: Two obstetricians independently assessed the CTG and ST traces of 41 fetuses with metabolic acidaemia at birth and 101 controls, blinded to group, outcome and all clinical data. They classified each CTG trace and ST analysis as abnormal or not abnormal, and whether there was indication to intervene according to the CTG or to the CTG + ST guidelines. If their classification differed, assessment by a third obstetrician determined the final classification. MAIN OUTCOME MEASURES: Rates of CTG and ST abnormalities and decisions to intervene. Rates of inter-observer agreement. RESULTS: CTG was classified as abnormal in 50% and ST in 63% of cases with acidaemia, and in 20% and 34% of controls, respectively. CTG abnormalities were judged to be indication for intervention in 45% and CTG + ST abnormalities in 56% of cases with acidaemia, and in 15% and 8% of controls, respectively. The proportion of agreement between the two initial observers was significantly higher for ST abnormalities (94%) than for CTG abnormalities (73%), and for indication to intervene according to CTG + ST (89%) than according to CTG alone (76%). CONCLUSIONS: The inter-observer agreement rate was higher for a decision to intervene based on CTG + ST than on CTG alone.     

Fetal heart rate variability changes and fetal behavioural cycles during labour

In a study of 301 consecutive fetal heart rate (FHR) recordings of greater than or equal to 6 h duration, consecutive episodes of low and high FHR variability consistent with cycles of quiet and active fetal behaviour were found in 38% of spontaneous and 68% of induced labours at term (P less than 0.0001). Quiet periods (episodes of low FHR variability) had durations of 12-93 min (mean 25, SD 11 min) and in 48% of cardiotocographs (CTGs) these episodes had a long-term variability of less than 5 beats/min. The implications of these findings are discussed in relation to the use of FHR recording for intrapartum surveillance.     

Fetal arrhythmia during pregnancy and labour.

The significance of fetal arrhythmia presenting during pregnancy and labour has been examined in 68 patients. The different types of rhythm disorders diagnosed included 61 extrasystoles, 6 atrioventricular blocks and 1 auricular fibrillation. Extrasystoles were not associated with acidosis or organic cardiac disease. Atrioventricular block, though not associated with fetal hypoxia, was occasionally associated with congenital cardiac failure.     

Fetal plasma catecholamine concentrations and fetal heart-rate variability during first stage of labour

Summary. Fetal heart-rate (FHR) variability was studied in 50 term fetuses during the first stage of labour. The variability was computed as an arbitrary index during a 20-min period preceding a fetal scalp blood sample which was used for the measurement of pH, adrenaline and noradrenaline. None of the fetuses was found to have a scalp blood pH<7.2. The short-term variability index was significantly correlated with the noradrenaline concentration in fetal blood, but the adrenaline levels which were generally very low showed no correlation with the variability values. There was no correlation between variability index and cervical dilatation or blood pH. We have shown previously high plasma catecholamine concentrations in the asphyxiated fetus with a decreased pH. In this study where fetal pH was normal a correlation between FHR variability and fetal scalp plasma noradrenaline levels was found. Thus an increased FHR variability might be an early sign of fetal distress when fetal pH is still normal.     

Fetal scalp pH and ST analysis of the fetal ECG as an adjunct to CTG. A multi-center, observational study

OBJECTIVE: To evaluate the relationships between scalp-pH and CTG plus ST waveform analysis of the fetal ECG (STAN) clinical guidelines as indicators of intrapartum hypoxia in term fetuses born with cord artery acidemia. STUDY DESIGN: Data from 6999 term deliveries monitored by the STAN (R) S 21 as part of an EU multi-center study on clinical implementation of the STAN methodology for intrapartum fetal surveillance were analyzed. We identified 911 cases where a scalp-pH was obtained, including 53 cases with cord artery acidemia (pH < 7.06). Lag times between ST events and scalp-pH and time to delivery were related to cord artery metabolic and respiratory acidosis and neonatal outcome. RESULTS: 43 fetuses were identified by CTG plus ST as being in need of intervention 31 (25-46) minutes before delivery (median, 95% Cl). In five, no indications were given and in another five there were inadequate data. Fifteen cases with metabolic acidosis required special neonatal care, all 14 cases adequately monitored on STAN had indications to intervene for 19 minutes or more. In 30 adequately recorded cases, fetal blood sampling (FBS) was obtained within the last hour of labor. In 22 cases, FBS was obtained 13 (7-24) minutes after STAN guidelines had indicated abnormality and in eight no ST changes had occurred at time of FBS. The corresponding FBS data were pH 7.10 (7.01-7.15) and pH 7.21 (7.08-7.31), respectively, P = 0.01. In cases of metabolic acidosis, scalp-pH fell 0.01 units per minute after a baseline T/QRS rise was recorded during the second stage of labor. Apart from one newborn that died at 2 h from E. Coli septicemia, none of the neonates were affected neurologically. CONCLUSION: Cardiotocography plus ST analysis provides accurate information about intrapartum hypoxia similar to that obtained by scalp-pH.     

Fetal distress and the condition of the newborn using cardiotocography and fetal blood analysis during labour

The efficacy of electronic fetal monitoring combined with fetal blood analysis during labour in identifying fetal distress was investigated in a retrospective study. Operative delivery for fetal distress diagnosed during labour was performed in 9% of 2659 deliveries. All had continuous fetal heart rate monitoring and 22% had a fetal scalp blood analysis. Operative delivery had been performed in 53% of the infants who were acidotic at birth (umbilical artery pH less than 7.20) and in 46% of those with a low modified Apgar score (less than 7). These results show that the use of continuous fetal heart rate monitoring and fetal scalp blood sampling detects fetal distress without resulting in a high rate of operative delivery.