Trend Detection in the Fetal Condition

Heart rate variation during fetal behavioural states 1 and 2

Fetal heart rate (FHR) variation was numerically assessed in relation to behavioural states in 34 normal near term fetuses, in order to study the normal ranges of FHR variation during state 1F and 2F and to determine possible factors influencing variation in these states. In all individuals 2-h recordings were made of fetal heart rate, and body and eye movements. FHR variation was quantified using the Sonicaid System 8000. During both 1F and 2F there was a large range in variation, with a wide overlap in variation between both states (mean 1-min range in pulse intervals 16-53 ms and 36-97 ms, respectively). In all fetuses variation was higher during 2F than during 1F. The large ranges in variation were mainly caused by differences in basal heart rate and the correlation coefficients between rate (beats/min) and variation were -0.68 and -0.49 for 1F and 2F, respectively. Other reasons for a relatively high FHR variation during 1F included 'pseudo' sinusoidal patterns related to fetal sucking or mouth movements and relatively flat periods sporadically interrupted by an acceleration. With the System 8000, periods of low and high variation are identified using fixed criteria. Because of the large overlap in variation between both states, these episodes poorly correlated with the underlying behavioural states. Objective identification of the heart rate patterns during states 1F and 2F requires incorporation of heart rate itself in the analysis. As yet, 'global' visual identification of heart rate patterns is superior to computer analysis in identifying the underlying fetal behavioural states.

Human fetal oxygenation (tcPo2), heart rate variability and uterine activity following maternal administration of meperidine

Fetal tcPo2 levels were measured in 10 patients following maternal administration of 50 mg of meperidine by intravenous route. About 3 minutes following injection of meperidine, tcPo2 values started to decline to reach the lowest value of 37 +/- 25% by 7 mins of injection. tcPo2 values recovered by about 15 mins following injection. These changes in fetal tcPo2 levels preceded transient minimal increase in FHR variability. The increase in FHR variability was followed immediately by a decrease in the indices of the FHR variability. The uterine activity began to decline below the predicted positive slope values shortly following injection of meperidine. This decline was maximum 15 mins post-injection, subsequently establishing a trajectory toward the positive values expected for unmedicated labor. Two patients receiving 25 mg intravenous meperidine demonstrated no decline in tcPo2 levels; however, in the patient receiving 75 mg of intravenous meperidine, the changes noted were similar to those observed following 50 mg of meperidine.

Analysis of heart rate and beat-to-beat variability: Interval difference index

The relationshp between the RR interval length (RR) and the RR interval-to-interval differences (RR differences) was investigated. Data on heart rate were obtained from 11 newborn infants in well-defined behavioral states undergoing polygraphy. It was found that the RR differences were strongly dependent on the RR interval length in all behavioral states. The relationship between the RR differences (y) and the interval length (RR) could be described by the equation y = alpha (RR-320)1.5 for the interval length in the investigated range from 375 to 605 msec. On the basis of this relationship the interval difference index (ID index) was constructed for the quantification of beat-to-beat heart rate variability. The ID index showed good independence from the long-term irregularity index (LTI index). Other statistical parameters proposed for the quantification of beat-to-beat heart rate variability are discussed and compared with the ID index.

Fetal heart rate variability as an indicator of fetal status

Numerous studies have shown the clinical usefulness of monitoring fetal heart rate (FHR) variability. Among the disorders associated with decreased FHR variability during labor are fetal asphyxia and acidosis and subsequent distress in the newborn. Among the factors that influence FHR variability are maternal fever, fetal immaturity, so-called fetal sleep, fetal tachycardia, and drug administration to the mother. The nonstress test, which analyzes FHR variability and accelerations of heart rate with fetal movements, may be as useful as the oxytocin challenge test for assessing FHR variability. Doppler ultrasonic cardiography exaggerates the amount of FHR variability. FHR patterns associated with progressive loss of beat-to-beat variability in the absence of maternal drug intake necessitate intervention.

Fetal baseline heart rate variability estimation. I. Comparison of clinical and stochastic quantification techniques

Baseline fetal heart rate variability is an important parameter in the evaluation of fetal status during the intrapartum period. Prior descriptions of variability have largely been either visual-subjective or stochastic in nature. Unfortunately, correlation between the two has not been substantiated. Sample heart rate tracings were evaluated for variability by a panel of nine experts. Interobserver agreement in the evaluation of variability was high; correlation between visual subjective and stochastic methods was low. The implications are discussed.

Computer analysis of fetal heart rate variation during normal pregnancy

Ninety-seven one-hour recordings of the abdominal fetal electrocardiogram (ECG) were made from 59 normal patients between 21 and 41 weeks of gestation. The heart intervals, measured between successive R-waves, were analysed by computer. The signal-to-noise ratio of the fetal ECG limited the precision of the interval measurements to approximately one millisecond. The characteristics of the baseline heart rate changed significantly as gestation advanced, the mean R-R interval, the standard deviation of the intervals and the standard deviation of the interval differences all increasing with gestation (p less than 0.001). In later gestation the baseline heart rate during periods of fetal rest differed significantly from that during periods of fetal activity; during rest the mean R-R interval was greater (p smaller than 0.001) and the standard deviations of the intervals and interval differences were smaller (p smaller than 0.001). Examination of the coefficient of variation of the heart intervals gave a result which contradicted the significance of this measurement as an index of fetal welfare as proposed by Curran and MacGregor (1970).