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).     

Effect of angiotensin infusion during pregnancy on fetal heart rate and on fetal activity

The angiotensin sensitivity test is of value in predicting patients at increased risk of pregnancy-induced hypertension and preeclampsia. Studies on the effects of angiotensin II on uterine blood flow in various species showed contradicting results. In the present study, 15 pregnant women were monitored by cardiotocography before, during and after an infusion of angiotensin II-amide (maximal infusion rates 6.3–23.2 ng · kg^?1 · min^?1). No remarkable changes in fetal heart rate, oscillatory frequency and amplitude, as well as in the number of accelerations and fetal movements could be observed. It may be concluded from these results that the fetal condition is not compromised by an angiotensin sensitivity test.     

Effect of gestational age on baseline fetal heart rate during the third trimester of pregnancy

Analysis of the fetal heart rate in 3,127 reactive nonstress tests revealed that the baseline rate decreased significantly between 28 and 41 weeks' gestation (6.4 beats per minute [4.5%]). Analysis of 235 women with two tests at least four weeks apart revealed that while the majority (51.1%) demonstrated a decrease, 26.8% experienced a rise in the baseline rate during the testing interval.     

Evaluation of the fetal movements and accelerations of fetal heart rate in twin pregnancy

In twin pregnancy, the fetal heart rates (FHR) of each fetus and uterine contraction were recorded simultaneously on a single recording chart by two cardiotocographs and a linear multichannel recorder. In addition, with a new technique, FHR and fetal movement (FM) signal bursts for each fetus were recorded similarly on a single recording chart by two ultrasonic Doppler actographs and an electronic polyrecorder. Simultaneous nonstress tests were done for 32 sets of twins at 28 to 41 weeks' gestation. The observed acceleration number in every gestational week increased till 38 weeks and this result was similar to that in singletons. Completely synchronous acceleration patterns in the 2 fetuses were observed in 654 recordings (31.4%) and asynchronous acceleration patterns in 1,108 recordings (53.1%). Simultaneous FHR and FM signal burst recordings were performed in 7 twin pregnancies. In about half of the 1,535 recordings, the FM signal bursts were synchronous between 2 fetuses, whereas they were asynchronous in the other half. Synchronous FM bursts in each gestational week decreased with time. Neurological independency between the twins was suggested by the results. The synchronous appearance of FM signal bursts with FHR accelerations of 2 fetuses was more pronounced in a uniovular twin than in a biovular twin.     

Evaluation of the accuracy of a new ultrasonic fetal heart rate monitor

An indirect Doppler fetal monitoring system has been developed and validated by computer comparison of simultaneous fetal heart rate (FHR) with Doppler and scalp ECG of high-risk patients during labor. The difference in measurement of FHR averaged 0.3 b.p.m., and 93 per cent of the Doppler FHR measures were within 10 b.p.m. of the ECG FHR. If interinstrument difference is discounted, 96 per cent were within 10 b.p.m. All types of decelerations and variability were well approximated. Doppler FHR from the instrument described may be relied upon as valid clinical information and may be obtained from over 90 per cent of labor patients with 93 per cent accuracy.     

Low human fetal heart rate variation in normal pregnancy

The fetal heart rates of 340 normal singleton pregnancies at 30-33 weeks gestation were screened using a microprocessor system on-line. Eleven fetuses (3.2%) with a heart rate variation less than the 5th centile were identified, of whom 10 were studied longitudinally. At 30-33 weeks the mean minute range of pulse intervals (a measure of fetal heart rate variation) was 31.4 (SE 1.5) ms compared with 51.0 (SE 3.4) ms in a randomly selected control group. The study group continued to have significantly lower fetal heart rate variation than controls on each of three subsequent occasions until delivery. There were no significant differences between the two groups in fetal outcome, which was good. This demonstrates that a small proportion of normal fetuses have consistently low heart rate variation, and helps to define the lower limit of the normal distribution of fetal heart rate variation. After delivery, there were no significant differences between heart rate or its variation between the two groups. We conclude that the lower prenatal heart rate variation in the study group was a consequence of the uterine environment.     

Sinusoidal fetal heart rate pattern during labor

Of 1280 consecutive fetuses monitored internally with a scalp electrode for at least 10 minutes during labor, 54 (4.2%) demonstrated the sinusoidal heart rate (SHR) pattern. Seven of these demonstrated the SHR pattern for more than 90 minutes. In six of these seven cases, the SHR pattern occurred during oxytocin administration. The SHR group did not differ from the 1226 fetuses not demonstrating the SHR pattern (NSHR group) in Apgar scores, incidence of other fetal heart rate abnormalities, or passage of meconium. The scalp pH was obtained from three fetuses in the SHR group and was above 7.30 in each. Alphaprodine administration during labor was associated with development of the SHR pattern, whereas other narcotic administration was not. The significance of "atypical" SHR pattern with increased amplitude is discussed, along with the need to adhere to strict definition of the SHR pattern.     

Variability analysis of fetal heart rate signals as obtained from abdominal electrocardiographic recordings

The present paper introduces an original method of digital signal processing for an automatic analysis of non-invasive abdominal ECG recordings on pregnant women starting from the 25th week of gestation. The procedure has been implemented on a DEC-VAX 750 digital computer at the Department of Electrical Engineering, Polytechnic of Milano and the signals are recorded at the Department of Obstetrics and Gynecology "L. Mangiagalli", University of Milano, Italy. The experimental results presented in here are still preliminary as only few cases have been considered up to now (about 20) and the goal of the paper is mainly focused on the algorithmic aspects of the whole procedure implemented in the computer and on the approach of heart rate variability (HRV) signal analysis both in the mother and in the fetus. Abdominal ECG lead processing is illustrated starting from the step of maternal (M) and fetal (F) QRS recognitions through linear digital filtering (derivative and low-pass FIR filter, Weber-Cappellini window) and weighted averaging techniques synchronized with maternal QRS's. Figure 1 a shows the original abdominal lead; figure 1 b the filtered signal for MQRS recognitions; figure 2 a the template of maternal cardiac cycle as obtained after the averaging operation synchronized with the instants of MQRS occurrence. The subtraction of the template results in the abdominal lead shown in figure 1 c in which the contribution of MECG is practically entirely reduced even in the case of MQRS and FQRS overlapping.(ABSTRACT TRUNCATED AT 250 WORDS)     

Computerized analysis of fetal heart rate variability using the matching pursuit technique as an indicator of fetal hypoxia during labor

Objective.?To determine whether the computerized analysis of fetal heart rate variability with the new matching pursuit technique can indicate fetal distress during labor.

Study design.?Eighty women were studied during the intrapartum period with external cardiotocography. In all cases, cord arterial pH and 5-min Apgar Scores were evaluated. Six cases that presented large segments of missing data were excluded from the study. The remaining 74 women were divided into two groups; 32 women with normal (Group A) and 42 women with non-reassuring FHR tracings (group B). Group B was divided in subgroup BI, including 24 women with pH > 7.20, and BII, including 18 women with pH < 7.20. In order to evaluate the FHR fluctuations, in different frequency ranges, we applied an adaptive time-frequency method, called Matching Pursuit. We estimated the power of the FHR signal in four frequency ranges.

Results.?The 5-min Apgar Scores were significantly lower in both subgroup BI and subgroup BII (p = 0.003 and p = 0.003 respectively). The Low Low Frequency (LLF) parameter appears to recognize better the cases with lower pH (sensitivity 78.5%, specificity 52.3%) than the cases with non-reassuring FHR (66.6%, 56.2). The sensitivity and specificity of the Very Low Frequency (VLF) parameter were 72.2% and 59% respectively in recognizing the cases with lower pH and 64.2% and 53.1% in recognizing non-reassuring FHR.

Conclusion.?Fetal hypoxia during labor can be recognized using the MP technique for the analysis of FHR signal power in the VLF and LLF frequency ranges. Since the analysis is feasible in real-time, it can be a useful tool for the intrapartum evaluation of fetal well-being.     

Electronic fetal heart rate monitoring during cesarean section

Fetal heart rate (FHR) response to cesarean section was studied in 65 patients. Induction of anesthesia, skin, fascial, peritoneal and bladder flap incisions were not associated with a change in FHR. Abdominal preparation was associated with FHR decelerations in 15% of cases. Myometrial incision was followed by FHR deceleration in 11% of cases. No correlation between the incision/delivery (I-D) interval and FHR changes was seen.     

Short term variability of fetal heart rate during pregnancies complicated by hypertension

Summary. The clinical significance of the differential index (DI), which describes the short term variability of fetal heart rate (FHR), in fetal surveillance was assessed in 202 hypertensive pregnancies. The analyses of FHR variability were made by a microprocessor-based on-line method using the abdominal fetal electrocardiogram as a triggering signal. The analysis was successful in 258 out of 323 trials (80%). Five perinatal deaths (2.5%) occurred in the whole series. Fetal distress developed in 47 out of 137 patients who had a successful FHR analysis within 1 week of delivery. The sensitivity of the antepartum DI in predicting fetal distress in labour was 46%, predictive value was 88% and specificity 97%. The risk of intrapartum fetal distress after a pathological DI was 4 times that after a normal DI (relative risk), which is highly significant.     

Computerized analysis of fetal heart rate variability using the matching pursuit technique as an indicator of fetal hypoxia during labor.

OBJECTIVE: To determine whether the computerized analysis of fetal heart rate variability with the new matching pursuit technique can indicate fetal distress during labor. STUDY DESIGN: Eighty women were studied during the intrapartum period with external cardiotocography. In all cases, cord arterial pH and 5-min Apgar Scores were evaluated. Six cases that presented large segments of missing data were excluded from the study. The remaining 74 women were divided into two groups; 32 women with normal (Group A) and 42 women with non-reassuring FHR tracings (group B). Group B was divided in subgroup BI, including 24 women with pH > 7.20, and BII, including 18 women with pH < 7.20. In order to evaluate the FHR fluctuations, in different frequency ranges, we applied an adaptive time-frequency method, called Matching Pursuit. We estimated the power of the FHR signal in four frequency ranges. RESULTS: The 5-min Apgar Scores were significantly lower in both subgroup BI and subgroup BII (p = 0.003 and p = 0.003 respectively). The Low Low Frequency (LLF) parameter appears to recognize better the cases with lower pH (sensitivity 78.5%, specificity 52.3%) than the cases with non-reassuring FHR (66.6%, 56.2). The sensitivity and specificity of the Very Low Frequency (VLF) parameter were 72.2% and 59% respectively in recognizing the cases with lower pH and 64.2% and 53.1% in recognizing non-reassuring FHR. CONCLUSION: Fetal hypoxia during labor can be recognized using the MP technique for the analysis of FHR signal power in the VLF and LLF frequency ranges. Since the analysis is feasible in real-time, it can be a useful tool for the intrapartum evaluation of fetal well-being.