Computerized analysis of fetal heart rate variation in postterm pregnancy: prediction of intrapartum fetal distress and fetal acidosis

The impact of umbilical and uterine artery Doppler indices on antenatal course, labor and delivery in a low-risk primigravid population

AIMS

To evaluate the impact of umbilical and uterine artery Doppler in the second and third trimester on antenatal course, labor and delivery in a low-risk primigravid population.

METHODS

Prospective recruitment of 1011 low-risk primigravidas with uterine and umbilical artery Doppler assessment at 22-24 weeks and 36 weeks. All mothers and infants were reviewed postnatally with a retrospective analysis of ultrasound and clinical outcome data.

RESULTS

Elevated uterine artery indices were associated with increased rates of threatened miscarriage, higher rates of pre-eclampsia (PET) and a higher incidence of fetal birth weight <2nd and 9th centile for gestation. Uterine artery pulsatility index (PI) >95th centile for gestation was associated with statistically higher rates of small-for-gestational age (SGA) infants. Elevated umbilical artery indices were associated with higher rates of induction of labor and a higher incidence of fetal birth weight infants <2nd and 9th centile for gestation. Umbilical artery PI >95th centile for gestation was associated with statistically higher rates of SGA infants.

CONCLUSION

Elevated uterine and umbilical artery indices are associated with higher rates of maternal and fetal disease.

Computerized analysis of fetal heart rate in pregnancies complicated by gestational diabetes mellitus, gestational hypertension, intrauterine growth restriction and premature rupture of membranes

OBJECTIVE

We aimed to compare individual fetal heart rate (FHR) indices, as determined by computer analysis of the tracing, in pregnancies complicated by gestational diabetes mellitus (GDM), gestational hypertension (PIH), intrauterine growth restriction (IUGR) and premature rupture of membranes (pPROM).

METHODS

The study population consisted of 100 pregnant women affected by GDM on diet therapy, 100 pregnant women affected by GDM on insulin therapy, 100 pregnant women affected by PIH, 100 pregnant women affected by IUGR, 100 with premature rupture of membranes far from the term (pPROM) and 100 normal pregnancies matched for age, parity and gestation as controls. The 30-min FHR tracing was analyzed by computer.

RESULTS

Baseline FHR, the duration of episodes of low variation and short-term variation was significantly higher in pregnancies complicated by gestational diseases than in controls; only in PIH, IUGR and pPROM were a significant reduction of the numbers of fetal movements.

CONCLUSIONS

Our study demonstrates that pregnancies complicated by gestational diseases do an impact on FHR. The alteration is slight but evident; it reflects fetal well-being. Computerized FHR tracing analysis may improve the clinical care and the timing of delivery.

Guidelines for the management of postterm pregnancy

A pregnancy reaching 42 completed weeks (294 days) is defined as postterm (PT). The use of ultrasound in early pregnancy for precise dating significantly reduces the number of PT pregnancies compared to dating based on the last menstrual period. Although the fetal, maternal and neonatal risks increase beyond 41 weeks, there is no conclusive evidence that prolongation of pregnancy, per se, is the major risk factor. Other specific risk factors for adverse outcomes have been identified, the most important of which are restricted fetal growth and fetal malformations. In order to prevent PT and associated complications routine induction before 42 weeks has been proposed. There is no conclusive evidence that this policy improves fetal, maternal and neonatal outcomes as compared to expectant management. It is also unclear if the rate of cesarean sections is different between the two management strategies. After careful identification and exclusion of specific risks, it would seem appropriate to let women make an informed decision about which management they wish to undertake. There is consensus that the number of inductions necessary to possibly avoid one stillbirth is very high. If induction is preferred, procedures for cervical ripening should be used, especially in nulliparous women. Close intrapartum fetal surveillance should be offered, irrespective of whether labor was induced or not.

Deceleration area of fetal heart rate trace and fetal acidemia at delivery: A case–control study

OBJECTIVE

To assess the correlation between the total deceleration area of the fetal heart rate (FHR) pre-delivery trace and intrapartum fetal acid-base status in a low risk population.

STUDY DESIGN

We analyzed the electronic fetal monitoring (EFM) traces of 26 pregnancies with fetuses presenting acidemia at delivery and those of thirty controls. All laboring patients had at least 1 hour of EFM without interruption. The deceleration area was calculated, after digital analysis, with Autocad System 2004.

RESULTS

We found that the number of decelerations (8.03 +/- 3.77 vs. 4.64 +/- 3.84) and the total deceleration area/hour (35.56 +/- 11.87 vs. 17.81 +/- 9.38) were significantly higher in the study group than in the control group.

CONCLUSIONS

Our results show that quantitative analysis of the deceleration areas by digitized cardiotocography may have a discriminative capacity to predict fetal acidemia at delivery.

Fetal distress evaluation using and analyzing the variables of antepartum computerized cardiotocography

OBJECTIVE

In this study, we tried to establish cut-off values for more than one parameters of computerized cardiotocography (c CTG) in the prediction of fetal distress during labor, using a group of pregnant women with low-risk pregnancies.

METHOD

A retrospective study was performed. Data were collected from 167 patients for measurements of fetal heart rate (FHR) variables and perinatal outcome. Computerized CTG was performed with an Oxford Sonicaid monitor with connection to a 8000 system for CTG spontaneous analysis. The following c CTG variables were considered: FHR, number of accelerations, the presence and the number of episodes of high and low variation, the number of decelerations, short-term variation (STV), peaks of contractions (per hour) and fetal movements assessed by maternal perception (per hour). Computerized CTG recordings started not earlier than the beginning of week 38 of gestation. Immediately after delivery, blood sample was collected from umbilical artery for umbilical artery blood gas analysis (UBGA). The main UBGA parameter in cord umbilical artery that was considered for analysis was pH. pH values<7.25 were considered as suspicious for acidemia and pH values>or=7.25 as normal.

RESULTS

Women suspicious for fetal distress during labor presented significantly lower fetal movements (P=0.026), accelerations (P=0.018), variability (P<0.001), number of high episodes (P<0.001), higher values of FHR baseline (P<0.001) and low episodes (P<0.001). Only the number of decelerations did not differ significantly between the two groups (P=0.545). The cut-off points of 5.00 for STV and 3.00 for high episodes were determined to classify women with fetal distress, which yielded high sensitivities (34 and 52%) and specificities (96.6 and 94.9%), with positive predictive values of 81.0 and 81.3% and negative predictive values of 77.4 and 82.2%, respectively.

CONCLUSIONS

In conclusion, we believe that not only STV but also other components of the cCTG, mainly the presence and the number of episodes of high variation, are related to pregnancy's outcome as measured by an umbilical artery pH.

The computerized fetal heart rate analysis in post-term pregnancy identifies patients at risk for fetal distress in labour

OBJECTIVE

To ascertain the diagnostic ability of a computerized fetal heart rate (FHR) analysis system in the identification of patients at risk of fetal distress in labour.

STUDY DESIGN

Three hundred and two healthy post-term pregnancies were enrolled in a retrospective, cross-sectional study and subdivided into two groups, with (n=42) or without (n=260) fetal distress in labour. The last computerized FHR recording before onset of labour was analyzed.

RESULTS

The two groups showed a significant difference only in FHR baseline and in percentage of small accelerations on total. The multivariate analysis showed that only the percentage of small accelerations was significantly related to the labour outcome. A higher diagnostic accuracy was obtained with use of neural network analysis, which allowed a sensitivity of 56%, specificity 91%, positive predictive value 53% and negative predictive value 92% with an overall accuracy of 86%.

CONCLUSIONS

The increase in FHR baseline and in small FHR accelerations can be major factors in the prediction of subsequent fetal distress in healthy term fetuses. Use of neural networks seems to further improve the ability of computerized FHR analysis in the prediction of intrapartum distress.

Screening for fetal well-being in a high-risk pregnant population comparing the nonstress test with umbilical artery Doppler velocimetry: a randomized controlled clinical trial

OBJECTIVE

The purpose of this study was to evaluate the ability of two different modes of antepartum fetal testing to screen for the presence of peripartum morbidity, as measured by the cesarean delivery rate for fetal distress in labor.

STUDY DESIGN

Over a 36-month period, all patients who were referred to the Fetal Assessment Unit at BC Women's Hospital because of a perceived increased fetal antepartum risk at a gestational age of > or =32 weeks of gestation were approached to participate in this study. Fetal surveillance of these women was allocated randomly to either umbilical artery Doppler ultrasound testing or nonstress testing as a screening test for fetal well-being. If either the umbilical artery Doppler testing or the nonstress testing was normal, patients were screened subsequently with the same technique, according to study protocol. When the Doppler study showed a systolic/diastolic ratio of >90th percentile or the nonstress testing was equivocal (ie, variable decelerations), an amniotic fluid index was performed, as an additional screening test. When the amniotic fluid index was abnormal (<5th percentile), induction and delivery were recommended. When the Doppler study showed absent or reversed diastolic blood flow or when the nonstress test result was abnormal, induction and delivery were recommended to the attending physician. Statistical comparisons between groups were performed with an unpaired t test for normally distributed continuous variables and chi(2) test for categoric variables.

RESULTS

One thousand three hundred sixty patients were assigned randomly to groups in the study; 16 patients were lost to follow up. Six hundred forty-nine patients received Doppler testing and 691 received nonstress testing. The mean number of visits for the Doppler test and nonstress test groups was two versus two, respectively. The major indications for fetal assessment included postdates (43%), decreased fetal movement (22%), diabetes mellitus (11%), hypertension (10%), and intrauterine growth restriction (7%). The incidence of cesarean delivery for fetal distress was significantly lower in the Doppler group compared with the nonstress testing group (30 [4.6%] vs 60 [8.7%], respectively; P <.006). The greatest impact on the reduction in cesarean deliveries for fetal distress was seen in the subgroups in which the indication for testing was hypertension and suspected intrauterine growth restriction.

CONCLUSION

Umbilical artery Doppler as a screening test for fetal well-being in a high-risk population was associated with a decreased incidence of cesarean delivery for fetal distress compared to the nonstress testing, with no increase in neonatal morbidity.

A computer system for the numerical analysis of nonstress tests

The development and clinical validation of a computer system for the numerical analysis of nonstress tests is reviewed, and recent improvements are reported. The analysis was developed by using a database of 73,802 nonstress test readings to provide a numerical definition of reactivity that is tailored to the gestational age of the fetus and independent of the presence of accelerations. When used at the bedside, the analysis minimizes monitoring time by alerting the operator when monitoring can be safely stopped because the fetal heart rate is normal. It also detects potentially sinister sinusoidal patterns and improves the quality of nonstress test readings by quantifying signal loss and, if significant, alerting the operator.

Nonstress testing and contraction stress testing

Antepartum fetal heart rate (FHR) testing, including the nonstress test and contraction stress test, has evolved in clinical usage over the past 3 decades. Although the nonstress test has become a standard of care in high-risk pregnancy, it has been modified by the use of fetal stimulation (vibroacoustic stimulation) and the addition of automated fetal movement recording (actocardiotocography). In all of its formats, antepartum FHR testing has been associated with reduction of preventable fetal loss. More recently, there have been attempts to improve test efficacy by computer-enhanced approaches.

Comparison of visual and computerized interpretation of nonstress test results in a randomized controlled trial

OBJECTIVE

This study tested the null hypothesis that the number of fetal surveillance tests and perinatal outcomes would not differ statistically between pregnancies randomized to visual or computerized interpretation of antepartum nonstress test results.

STUDY DESIGN

A prospective, randomized controlled trial was conducted, which required a sample size of 404 patients. By using a random-number table with assignment codes concealed in opaque envelopes, half of the patients were randomized to computerized interpretation of nonstress test results and half to standard visual interpretation of nonstress test results. The amount of antepartum testing and the perinatal outcome were measured and compared between the groups. Logistic regression analysis was used to control for maternal risk factors while morbidity differences between the 2 groups were assessed.

RESULTS

The 2 randomized groups were similar at baseline, but the computerized interpretation group had significantly fewer biophysical profiles compared with the visual interpretation group (1.3 +/- 1.8 vs 1.9 +/- 2.1; P =.002). The patients in the computerized interpretation group spent less time per test than patients in the visual interpretation group (12 vs 20 minutes; P =.038). After the 5 pregnancies with congenital anomalies were excluded, the overall perinatal outcome was similar in the 2 groups. The computerized interpretation group, however, had a slightly lower proportion of infants who required >/=2 days of neonatal intensive care (7.4% vs 12.4%; P =.086; odds ratio, 0.56; 95% confidence interval, 0.29-1.09). The average number of neonatal intensive care days was also slightly lower in the computerized interpretation group (0.4 vs 0.9; P =.105). Neither of these variables was statistically significant.

CONCLUSIONS

Computerized interpretation of nonstress test results is associated with fewer additional fetal surveillance examinations, less time spent in testing, and a similar length of stay in the neonatal intensive care unit compared with standard visual interpretation.

Computerised evaluation of fetal heart rate in post-term fetuses: long term variation

Computerised fetal heart rate records were obtained between 1987 and 1993 using the Sonicaid System 8000 for a cross-sectional study of postdates fetal heart rate variation; 567 singleton pregnancies at 41 and 43 weeks provided 1502 records. In all cases gestational age had been verified by ultrasound examination in early pregnancy. The mean minute range of the long term pulse interval variation, which is known to be correlated with fetal oxygenation was found to decrease progressively from an average value of 48.5 ms at 41 weeks to 46.4 ms and 42.4 ms at 42 and 43 or more weeks, respectively. When conservative management of postdate pregnancies is chosen, accurate measurements are needed to follow the evolution of fetal condition. Reference values for calculated pulse interval variation at later gestational ages are now provided.

Association between a low umbilical artery pulsatility index and fetal distress in labor in very prolonged pregnancies

OBJECTIVE

To investigate the association between fetal, umbilical and uterine circulatory changes and adverse perinatal findings in very prolonged pregnancies.

STUDY DESIGN

44 women proceeding to 43 completed weeks of gestation with the intention of a trial of vaginal delivery were studied prospectively with ultrasound Doppler velocimetry. An intensified fetal surveillance was routinely commenced at 42 weeks and only uncomplicated pregnancies were allowed to proceed. The endpoint perinatal measures were oligohydramnios, fetal meconium release, fetal distress in labor and birth asphyxia. Flow variables in different groups were compared with the Mann-Whitney U test, Student's unpaired t-test, Wilcoxon signed-rank matched-pairs test, Fisher's exact test and contingency table analysis, and a two-tailed P value <0.05 was considered statistically significant.

RESULTS

The umbilical artery pulsatility index was significantly lower in cases of fetal meconium release (n=12) and fetal distress (n=7). The umbilical venous flow velocity was significantly lower in cases of meconium, and the fetal aortic volume flow significantly higher in cases of fetal distress. No significant flow changes were found in connection with oligohydramnios (n=5) and birth asphyxia (n=2). Uterine flow was not significantly affected in any group.

CONCLUSIONS

In very prolonged pregnancies, fetal distress in labor was not associated with an increased placental vascular resistance. In contrast to previous reports, the umbilical artery pulsatility index was low in cases of fetal distress and meconium release. The etiology is unknown, but a subclinical fetal hypoxia might have triggered a vasodilation of placental vessels. Vasodilation at an unchanged volume flow could also explain the decrease of umbilical venous flow velocity. The increased aortic volume flow indicates an increase of cardiac output in fetuses later developing distress in labor.

Fetal heart rate patterns in pregnancies complicated by maternal diabetes

OBJECTIVE

To compare the fetal heart rate (FHR) pattern between fetuses of well controlled diabetic and non diabetic mothers using a computerized analysis of FHR.

STUDY DESIGN

Weekly fetal surveillance was performed in 99 fetuses of mothers with diabetes class A, 21 fetuses of mothers with diabetes class B-R, and 55 fetuses of non-diabetic women, starting at 30 weeks' gestation. All diabetic patients were well controlled. Fetal surveillance included a computerized analysis of the FHR, umbilical and uterine Doppler velocimetry, and a biophysical profile. Changes of FHR variation, frequency of FHR accelerations, and umbilical and uterine Doppler velocimetry were calculated using a regression analysis for each patient. The average slopes and the intercept at 30, 34, and 38 weeks' gestation of these variables were compared among the three groups.

RESULTS

The slope of FHR variation and the frequency of accelerations had a lower rate of increase during the third trimester in fetuses of mothers with diabetes class A (0.84 +/- 0.25 ms/week and 0.06 +/- 0.02/20 min/week, respectively) compared with fetuses of non-diabetic mothers (1.34 +/- 0.55 ms/week and 0.5 +/- 0.1/20 min/week, respectively). In fetuses of mothers with diabetes class B-R, FHR variation did not change with gestation (-0.011 +/- 0.2 ms/week) with a small increase in the frequency of accelerations (0.02 +/- 0.004/20 min/week). While no differences were observed at 30 weeks' gestation, FHR variation and the frequency of accelerations were significantly reduced at 34 weeks' gestation in fetuses of mothers with diabetes class B-R compared with fetuses of non-diabetic mothers (P < 0.01). At 38 weeks' gestation, fetuses of mothers with diabetes class B-R and diabetes class A had both significantly reduced FHR variation as well as frequency of accelerations compared with fetuses of non-diabetic mothers (P < 0.01). The rate of decrease of the umbilical and uterine artery S/D ratios were similar among the three groups.

CONCLUSIONS

The FHR pattern appears to be different in fetuses of well controlled diabetic mothers when related to fetuses of non-diabetic mothers. Disease specific standards should be considered for interpretation of FHR patterns in diabetic pregnancies.

Developments in CTG analysis

FHR monitoring has been the subject of many debates. The technique, in itself, can be considered to be accurate and reliable both in the antenatal period, when using the Doppler signal in combination with autocorrelation techniques, and during the intrapartum period, in particular when the FHR signal can be obtained from a fetal ECG electrode placed on the presenting part. The major problems with FHR monitoring relate to the reading and interpretation of the CTG tracings. Since the FHR pattern is primarily an expression of the activity of the control by the central and peripheral nervous system over cardiovascular haemodynamics, it is possibly too indirect a signal. In other specialities such as neonatology, anaesthesiology and cardiology, monitoring and graphic display of heart rate patterns have not gained wide acceptance among clinicians. Digitized archiving, numerical analysis and even more advanced techniques, as described in this chapter, have primarily found a place in obstetrics. This can be easily explained, since the obstetrician is fully dependent on indirectly collected information regarding the fetal condition, such as (a) movements experienced by the mother, observed with ultrasound or recorded with kinetocardiotocography (Schmidt, 1994), (b) perfusion of various vessels, as assessed by Doppler velocimetry, (c) the amount of amniotic fluid or (d) changes reflected in the condition of the mother, such as the development of gestation-induced hypertension and (e) the easily, continuously obtainable FHR signal. It is of particular comfort to the obstetrician that a normal FHR tracing reliably predicts the birth of the infant in a good condition, which makes cardiotocography so attractive for widespread application. However, in the intrapartum period, many traces cannot fulfil the criteria of normality, especially in the second stage. In this respect, cardiotocography remains primarily a screening and not so much a diagnostic method. As long as continuous monitoring of fetal acid-base balance has not been extensively tested in clinical practice, microblood sampling of the fetal presenting part (Saling, 1994) is a useful adjunct. The problem with non-normal tracings is that their significance is very often unclear. They may indicate serious fetal distress, finally resulting in preventable destruction of critical areas in the fetal brain and damage to various organs; or, on the contrary, they may indicate temporary changes in cardiovascular control as a reaction to the intermittent effects on fetal haemodynamics of, for example, uterine contractions, whether or not in combination with partial or complete compression of umbilical cord vessels or the vessels on the chorionic plate (van Geijn, 1994). Many factors influence the FHR and its variability, which further complicates the interpretation of FHR patterns; some have been discussed here in some detail. Undoubtedly, there is a need for quantitative and objective FHR analysis, as long as it does not lead to erroneous results. Close collaboration between engineers and clinicians is a prerequisite for further advances in this field. Decision support systems certainly have a future but only if they are able to take into account a large set of clinical data and can combine it with data obtained from FHR signals and other parameters referring to the fetal condition, such as fetal growth, Doppler velocimetry, amniotic fluid volume and biochemical and biophysical data obtained from the mother. Basic technical concepts inherent in computerized CTG analysis, such as sampling rate (Chang et al, 1995), signal loss, artefact detection (van Geijn et al, 1980), further processing of intervals, archiving in digitized format and monitor display, should receive considerable attention. There is still a long way to go until decision support systems find their way into obstetric practice. Further developments can only be achieved thanks to efforts of many basic and clinical researchers, wo

Central and peripheral haemodynamic changes in post-term fetuses: correlation with oligohydramnios and abnormal fetal heart rate pattern

OBJECTIVE

To assess the hypothesis that the occurrence of oligohydramnios and abnormal fetal heart rate (FHR) pattern in post-term fetuses is associated with impaired fetal cardiac function.

DESIGN

A cross sectional study was performed on post-term and term fetuses. Fetal tests included a computerised analysis of the FHR, a biophysical profile and Doppler studies of the abdominal aorta, umbilical artery, middle cerebral artery and the fetal heart. Pulsatility index (PI) was calculated from the abdominal aorta, umbilical and middle cerebral artery flow velocity waveforms. Peak velocity, velocity time integral (VTI), E:A ratio, and heart rate (HR) were calculated from the flow velocity waveforms obtained from the aortic and pulmonic outflow, and from the mitral and tricuspid valves.

SETTING

Maternal fetal laboratory, Department of Obstetrics.

SAMPLE

One hundred and twenty post-term and 42 term fetuses.

RESULTS

Only the tricuspid E:A ratio was significantly higher (P < 0.05) in post-term fetuses with a normal amniotic fluid index compared with term fetuses. Post-term fetuses with an abnormal amniotic fluid index had a significantly lower aortic peak velocity (P < 0.01), aortic VTI x HR (P < 0.01), and mitral VTI x HR (P < 0.05) compared with post-term fetuses with a normal amniotic fluid index or compared with term fetuses. Post-term fetuses with reduced FHR variation had a significantly lower aortic peak velocity (P < 0.01), pulmonic peak velocity (P < 0.05), aortic VTI x HR (P < 0.01), pulmonic VTI x HR (P < 0.05) and a significantly lower mitral VTI x HR (P < 0.05) when compared with post-term fetuses with normal FHR variation. Similar results were obtained in comparing fetuses with normal and adverse perinatal outcome.

CONCLUSION

The occurrence of oligohydramnios and abnormal FHR pattern in post-term fetuses appears to be associated with impaired fetal cardiac function. This finding should allow further investigations of post-term fetuses.