Antepartum fetal heart rate monitoring: I. A semi-quantitative evaluation of the ‘non-stressed’ fetal heart rate

1964 recordings (from 246 patients) were analysed on the basis of a semi-quantitative evaluation of base-line heart rate variability. All the tracings were obtained in the antepartum period, between the 20th wk of pregnancy and prior to the onset of labour. None of the recordings were made during labour or after induction of uterine activity so that a ‘non-stressed’ fetal heart rate test was obtained in every case. The percentage of flat tracing in each recording and the presence of sinusoidal patterns were compared with the neonatal outcome. When the tracings included a more than 50% flat pattern, 81.8% of the babies were distressed at birth. When a less than 50% flat recording was present only 11.4% of the neonates were distressed. Sinusoidal patterns were more frequently associated with abnormal tracings including those with more than 50% flat recordings. The presence of sinusoidal features did not significantly influence the neonatal outcome for tracings with a less than 50% anomaly: conversely sinusoidal patterns superimposed on a more than 50% flat tracing were predictive of fetal compromise and neonatal distress in 100% of the cases. These results allow to advocate the use of ‘non-stressed’ antepartum fetal heart rate monitoring, as a reliable test in the management of high risk pregnancies.     

Computerised antenatal fetal heart rate recordings between 24 and 28 weeks of gestation

Objective To assess computerised fetal heart rate recordings between 24 and 28 weeks of gestation for gestation related differences.
Design Prospective, cross sectional observational study.
Setting Liverpool Women's Hospital.
Population 112 women: 28 at 27 weeks, 30 at 26 weeks, 27 at 25 weeks and 27 at 24 weeks of gestation, respectively.
Methods Fetal heart recordings of 60 minutes duration were performed once in each pregnancy using the System 8000 fetal heart rate programme (System 8000, Oxford Sonicaid Ltd, Chichester, UK). For each gestational age, records were analysed for short term variation, basal heart rate, accelerations and time spent in high episodes.
Results The mean short term variation increased with gestation (   P =0.05  ). No record had a short term variation <4 msecs. There was no relationship between heart rate and increasing gestation. The mean number of accelerations per record increased with increasing gestation (   P <0.01  ). 20% of recordings showed no accelerations  >15 bpm  . The mean duration spent in episodes of high variation increased with gestation (   P =0.05  ). 13% of recordings showed no time spent in high episodes. All fetuses had normal outcomes at delivery.
Conclusions Absence of episodes of high variation or absence of accelerations is not an abnormal finding at lower gestations. The standard threshold of 4 msecs for short term variation appears to remain valid at lower gestations. These differences should be considered when using computerised CTG analysis at early gestations.     

The relationship between fetal heart rate accelerations, fetal movements, and uterine contractions

The association between fetal heart rate (FHR) accelerations and fetal movements during uterine contractions was studied in 52 pregnant women near term or at the beginning of labor. FHR and uterine contractions were recorded by tococardiograph. At the same time, fetal movements, whether associated or not with contractions, were viewed by real-time ultrasound. During uterine contractions, 95.5% of the FHR accelerations were associated with fetal movements. Also, 90.9% of the accelerations which appeared when the uterus was not contracting were associated with fetal movements. Fetal movements were not seen in 91% of uterine contractions which were not associated with FHR accelerations. The suggestion is made that uterine contractions stimulate both fetal movements and FHR accelerations.     

The relationship between antepartum fetal heart rate, intrapartum fetal heart rate, and fetal acid-base status

The relationships between antepartum baseline fetal heart rate, baseline variability, accelerations, decelerations, and fetal movement and intrapartum fetal heart rate, fetal acid-base assessment at delivery, and Apgar scores 1 and 5 minutes after delivery were studied in 290 mature pregnancies. There was a significant relationship between antepartum and intrapartum baseline fetal heart rate and baseline variability. There was no relationship between antepartum and intrapartum accelerations or decelerations. There was no correlation between antepartum fetal heart rate or fetal movement and fetal acid-base status at delivery or Apgar scores 1 and 5 minutes after delivery. There was a trend for decreased accelerations and decreased fetal movements to be associated with a low Apgar score 1 minute after delivery.     

The relation between fetal heart rate accelerations and fetal movements

Fetal heart rate (FHR) accelerations associated with fetal movements is considered a sign of fetal well-being. Fetal movements as felt by the pregnant woman and visualized by real-time ultrasonography were correlated to FHR accelerations in 52 normal and high-risk pregnant women. All fetal movements felt by the mother or seen in the real-time ultrasonography were associated with large FHR accelerations (more than 15 beats per minute lasting 15 seconds or more) or small accelerations (fewer than 15 beats per minute). The large accelerations were associated with 78.6% of fetal movements felt by the mother and 99.6% of fetal movements seen by real-time ultrasonography. The small accelerations were associated with 52.9% of fetal movements felt by the mother and 82.4% of fetal movements seen by ultrasonography. Mothers felt 75.7% of fetal movements seen by real-time ultrasonography. It was concluded that fetal movements could be verified by existence of large accelerations on the FHR tracing.     

The relationship between uterine contractions, fetal movements and fetal heart rate patterns in the active phase of labor

The relationship between fetal movements, fetal heart rate and uterine contractions was studied with a computerized system in 18 parturients during the active phase of labor. 80% of FHR accelerations and 39% of uterine contractions were associated with fetal trunk movements. The probability of association was greater in longer movements and larger accelerations. 98% of fetal movements which lasted 10-15 s, 98% of accelerations with an amplitude of 25-30 bpm and 96.4% of accelerations with a duration of 40-50 s were associated with fetal trunk movements.     

Relation between fetal heart rate accelerations, fetal movements, and fetal breathing movements

The presence of fetal heart rate (FHR) accelerations is considered a sign of fetal well-being. Fetal body and breathing movements, as visualized by real-time ultrasound, were correlated to FHR accelerations in 16 high-risk pregnancies. The association between FHR accelerations (greater than 15 beats/min lasting 15 sec or more) and the different fetal behavioral states is described.     

Limitations of autocorrelation in fetal heart rate monitoring

Fetal heart rate monitors that use autocorrelation of the ultrasonic fetal signal usually produce a cleaner fetal heart rate record than that obtainable with conventional ultrasonic fetal monitors. However, since the autocorrelation function will emphasize any periodic signal originating from the fetus or the mother, in clinical situations the resultant fetal heart rate tracing may contain spurious data. To illustrate the limitations of the autocorrelation technique in fetal monitoring, we compared the autocorrelated ultrasound fetal heart rate records from 23 patients in active labor with the simultaneously recorded direct scalp fetal electrocardiogram tracings. The results indicate that every hour of recording contained, on the average, five instances in which data were missing (range, 0 to 13), four in which data were added (range, 0 to 23), and seven instances in which data were absent for greater than 1 minute (range, 0 to 26). The potential problem of misinterpretation of autocorrelated fetal heart rate data is discussed.     

Fetal vibratory acoustic stimulation in twin gestations with simultaneous fetal heart rate monitoring

Sixteen vibratory acoustic stimulations were performed in seven normal twin gestations with continuous simultaneous recordings of each fetal heart rate response. All stimulations led to immediate synchronous fetal heart rate accelerations in both fetuses. This is in contrast to coinciding, yet nonsynchronous, spontaneous fetal heart rate accelerations that occur naturally. This observation suggests that different mechanisms are responsible for spontaneous and evoked fetal movements in twin gestations.     

Pattern of the normal human fetal heart rate

With an improved method for fitting baselines to human fetal heart-rate traces, the patterns of episodic variations, accelerations and decelerations were similar in 215 64-min records from normal pregnancies and in 95 with mild hypertension and normal outcome. The change in signal loss with gestational age, by Doppler ultrasound for recording heart rate, was entirely due to the greater loss in episodes of high heart-rate variation. The changes in the numbers and sizes of accelerations and decelerations with gestational age were described. There were many records which had only one or no acceleration at 28-33 weeks gestation (16.2%) or 34-41 weeks (7.3%). However, only two (0.7%) had episodes of high heart-rate variation lasting less than 10 min from 28 weeks onwards. The presence of these episodes, with clusters of fetal movements, is therefore likely to be a better numerical index of normality.     

Pattern of the normal human fetal heart rate

Summary. With an improved method for fitting baselines to human fetal heart-rate traces, the patterns of episodic variations, accelerations and decelerations were similar in 215 64-min records from normal pregnancies and in 95 with mild hypertension and normal outcome. The change in signal loss with gestational age, by Doppler ultrasound for recording heart rate, was entirely due to the greater loss in episodes of high heart-rate variation. The changes in the numbers and sizes of accelerations and decelerations with gestational age were described. There were many records which had only one or no acceleration at 28–33 weeks gestation (16.2%) or 34–41 weeks (7.3%). However, only two (0.7%) had episodes of high heart-rate variation lasting <10 min from 28 weeks onwards. The presence of these episodes, with clusters of fetal movements, is therefore likely to be a better numerical index of normality.     

Intrapartum fetal heart rate patterns in the prediction of neonatal acidemia

OBJECTIVE: This study was undertaken to correlate changes in the intrapartum electronic fetal heart rate patterns with the development of significant neonatal acidemia. STUDY DESIGN: We identified 488 fetuses at a gestational age of >37 weeks' gestation who had continuous electronic fetal monitoring during labor for the last 2 hours and umbilical artery cord gas analysis performed at delivery. One investigator blinded to the cord gas outcome reviewed all 488 tracings using the National Institute of Child Health and Human Development guidelines for fetal heart rate monitoring. All fetal heart rate tracings with bradycardia were removed from further analysis. The patients were placed in six groups, depending on the absence or presence of normal variability (amplitude >5 beats) during the last hour of monitoring combined with the absence of decelerations or the presence of variable or late decelerations. The relationship between changes in variability and the outcome variables of pH and base deficit in the six groups was assessed with analysis of variance and chi(2) test. Significance was set at the P <.05 level. RESULTS: Patients with normal variability and accelerations, even in the presence of late decelerations or variable decelerations, maintained an umbilical artery pH 7.0 or greater in more than 97% of cases. In the presence of minimal/absent variability (amplitude <5) for at least an hour, the incidence of significant acidemia (pH <7.0) ranged from (12%-31%). CONCLUSION: The most significant intrapartum fetal heart rate parameter to predict the development of significant acidemia is the presence of minimal/absent variability for at least 1 hour as a solitary abnormal finding or in conjunction with late decelerations in the absence of accelerations. Urgent delivery should be considered in these cases after appropriate ancillary testing.     

Automated analysis of near-term antepartum fetal heart rate in relation to fetal behavioral states: the Sonicaid System 8000.

Fetal heart rate and fetal movements were recorded in 16 uncomplicated near-term pregnancies. The recordings were used to evaluate a system for automated fetal heart rate analysis (Sonicaid System 8000). Fetal rest-activity patterns were considered in the analysis. The mean duration of C2F periods "active sleep," 33 minutes) was significantly greater than that of C1F periods ("quiet sleep," 19 minutes) (p less than 0.001). The incidence of accelerations and decelerations and the overall fetal heart rate variations were greater during C2F than during C1F (p less than 0.001). In 11 of 16 C1F periods, the system classified the fetal heart rate variation as "questionable" or "abnormal." Episodes of high variation were identified in only 3 of 16 C1F periods, but they were found in all 18 C2F periods. Episodes of low variation were identified in 14 of the 16 C1F periods but were not found in any C2F periods. During C2F periods, the system's criteria of normality were met in all cases but one; they were not met during any of the C1F periods. Thus the diagnosis of fetal distress should not be based merely on the absence of accelerations, low fetal heart rate variation, or absence of episodes of high variation in recordings with a duration of less than 45 minutes.     

The extent of fetal heart rate accelerations associated with fetal body movements in relation to the duration of fetal body movement

The temporal relations between fetal body movements and associated fetal heart rate accelerations were shown as the ratios of duration of acceleration or acceleration amplitude and the duration of associated fetal body movements in 44 normotrophic and 40 hypotrophic fetuses (body weights within the 6th to 10th percentiles, n = 19, and less than or equal to the 5th percentile, n = 21) between the 36th and 40th gestational weeks. Related to the duration of associated fetal body movements, hypotrophic fetuses proved to have gradually smaller heart rate accelerations than normotrophic fetuses. Moreover, the acceleration parameters duration and amplitude were dependent on the relative duration of fetal body movements. Short fetal body movements were accompanied by fetal heart rate accelerations of relatively highest degree and vice versa. As a consequence, no comparison is possible between temporally different fetal body movements and their associated heart rate accelerations. Of the two acceleration parameters duration and amplitude, the inclusion of the accelerations amplitude in the above mentioned ratio yielded the most obvious results. Taking into consideration that fetuses with intrauterine growth retardation are often in a state of chronic hypoxia, the ratios of acceleration amplitude and durations of associated fetal body movements indicated different degrees of this metabolic situation.     

Heart rate variation and movement incidence in growth-retarded fetuses: the significance of antenatal late heart rate decelerations

In 37 intrauterine growth-retarded fetuses, combined 1-hour recordings of fetal heart rate and body movements were made within 24 hours of elective cesarean section. Fetal body movements were recorded simultaneously by use of real-time ultrasound. The study group was divided into two subgroups, according to the presence (n = 29) or absence (n = 8) of antepartum late heart rate decelerations. Correlations were made with umbilical blood gas values obtained immediately after cesarean section. Baseline heart rate variation was reduced below the normal range in 88% of the intrauterine growth-retarded fetuses with decelerations but in only 37% of the group without decelerations. A reduction in fetal heart rate accelerations and body movements and an increase in mean heart rate also were observed only in the group with decelerations. Late heart rate decelerations were associated with low PO2 values in both umbilical artery and vein. It is concluded that in intrauterine growth-retarded fetuses reduced heart rate variation and movement incidence correlate with the presence of late heart rate decelerations before birth and with hypoxemia at birth.     

Longitudinal measurements of fetal breathing, body movements, heart rate, and heart rate accelerations and decelerations at 24 to 32 weeks of gestation

Fetal breathing, fetal body movements, fetal heart rate, and fetal heart rate accelerations and decelerations were studied longitudinally in healthy fetuses between 24 and 32 weeks' gestation in the second and third hour following an 800 kcal maternal meal. The expected increase in fetal breathing following a maternal meal was not seen until fetuses were at 30 to 32 weeks' gestation. The number of body movements decreased and the interaction between body movements and fetal heart rate accelerations became more evident as fetuses became older. Fetal heart rate decelerations increased with gestational age, and the relative proportion of total decelerations that were either associated with body movements or were part of a deceleration/acceleration/deceleration complex increased from 24 to 32 weeks' gestation. The data support the hypothesis that gestational age is an important variable to consider when interpreting biophysical measurements in the human fetus at 24 to 32 weeks' gestation. Fetal body movements may be the single most important measurement of fetal health at these gestational ages.     

Course and predictive value of fetal heart rate parameters

The present study concerns the developmental character of the fetal heart rate (FHR) pattern and the implications of predicting the perinatal outcome. Data from 443 patients undergoing 2193 nonstress tests were analyzed retrospectively. We found a significant increase of accelerations more than 15 beats/min, of accelerations associated with fetal movements, of fetal movements registered by the tocotransducer, the frequency of oscillations, and of the Fischer score values throughout gestation. The number of short FHR decreases and the mean baseline level declined throughout gestation. A long duration of absent or reduced baseline variability registered even 6 weeks before delivery was associated with low Apgar score values. Late decelerations and contractions registered early in pregnancy were also correlated to a poor outcome. Tachycardia and a low number of accelerations were only correlated to a poor perinatal outcome shortly before the delivery. Fetal movements not associated with FHR accelerations were an early indicator of a poor neonatal outcome. Scoring systems did not generally improve the predictive value of FHR patterns.     

Coupling of fetal movement and fetal heart rate accelerations as an indicator of fetal health.

OBJECTIVE: The purpose of this study was to determine the clinical value of identified coupling of fetal heart rate (FHR) accelerations (more than five beats per minute for any duration) with objectively detected fetal movements. METHODS: One hundred sixty-six patients underwent routine fetal testing using a Doppler device that recognized both FHR and fetal movements. The coupling index was determined to be the percentage of fetal movements associated with FHR accelerations, and various coupling indices were compared with nonstress test (NST) results. RESULTS: A coupling index above 25% and below 75% compared well with the traditional NST by standard epidemiologic criteria and by the kappa statistic. CONCLUSION: Coupling of even small FHR accelerations and fetal movements could substitute for or replace the NST in antenatal screening.     

Maternal position during non-stress test and fetal heart rate patterns

OBJECTIVE: The aim of the study was to determinate whether maternal position during the non-stress test (NST) in different weeks of pregnancy influences fetal heart rate patterns. MATERIALS AND METHODS: A total of 1055 NST lasting 30 min were performed in 368 autochthonous mothers with low-risk pregnancies. On the basis of maternal position during the test we divided into three groups: reclining, sitting, and walking. The cardiotocographic parameters considered were: number of minutes of reactive NST with minimum length, number of fetal movements, fetal heart rate baseline, number of large accelerations, number of dubious NST, and number of variable decelerations. RESULTS: Fetal heart rate patterns in low-risk pregnancies were studied using NST in different gestational ages and in different maternal positions. Differences in heart rate were found in relationship to both gestational age and maternal position. The minimum length of NST necessary to record at least three large accelerations was significantly different in relationship to both gestational age and maternal position. The number of fetal movements perceived by the mother was greater in the reclining position than in sitting or walking. Together with the progression of pregnancy, the number of dubious NST decreased in all subgroups, especially in the sitting position. The greatest number of variable decelerations was observed in the reclining position and it was increased with pregnancy progression. The NST duration did not vary greatly in the reclining position, but in the sitting position or during walking, the time taken to record the three large accelerations required to define the trace as reactive, decreased significantly with the progression of pregnancy CONCLUSIONS: Non-stress test in sitting position or during walking should be encouraged because fetal reactivity is more quickly observed.