Marked fetal acidosis and specific changes in power spectrum analysis of fetal heart rate variability recorded during the last hour of labour

OBJECTIVE

To assess whether intrapartum acidosis affects specific components of fetal heart rate variability.

DESIGN

Prospective clinical study.

SETTING

Twelve Nordic delivery units.

SUBJECTS

Fetal heart rate variability was studied in 334 fetuses divided into two groups according to cord pH value: the acidotic group (cord arterial pH < 7.05 at birth, n= 15) and the control group (cord arterial pH > or =7.05 at birth, n= 319).

METHODS

In spectral analysis of fetal heart rate variability, frequencies were integrated over the total frequency band (0.04-1.0 Hz), low-frequency band (0.04-0.15 Hz) and high-frequency band (0.15-1.0 Hz). We also calculated the low-to-high frequency ratio.

MAIN OUTCOME MEASURES

The spectral bands of fetal heart rate variability were compared between the acidotic and control fetuses.

RESULTS

We found that during the last hour of monitoring, baseline fetal heart rate gradually decreased, whereas total, low-frequency and high-frequency fetal heart rate variability initially increased but then, near the delivery, decreased in the acidotic fetuses when compared with the controls. Low-to-high frequency ratio was greater in the acidotic group during the whole study period (P= 0.002). Cord artery pH was inversely associated with total fetal heart rate variability (P < 0.001), low-frequency fetal heart rate variability (P < 0.001) and low-to-high frequency ratio (P= 0.004).

CONCLUSIONS

Marked fetal acidosis was associated with frequency-specific changes in fetal heart rate variability as reflecting the compensation ability of autonomic nervous activation during the last hour of labour.

The quality of intrapartum fetal heart rate monitoring

OBJECTIVE

To determine the quality of fetal heart rate (FHR) recordings during the first and second stage of labor by quantifying the amount of fetal signal loss in relation to the method of monitoring: external ultrasound or directly via a scalp electrode.

STUDY DESIGN

Analysis of 239 intrapartum recordings stored between 1 January 2001 and 1 July 2001 from consecutive deliveries at the Vrije Universiteit Medical Center in Amsterdam. Singletons delivered via the vaginal route were included in the study. FHR recordings had duration of at least 1h prior to birth of the infant. Subdivision in three groups took place on the basis of the recording technique which had been used; i.e. ultrasound, scalp electrode or a combination of both methods. FHR data was obtained using HP-M1350 cardiotocographs. The status (pen on, pen off, maternal signal) and the mode of the signals were acquired. The duration of pen lifts and maternal signals was divided by the total duration of the recording. Statistical analyses were performed with the Mann-Whitney U-test and the Wilcoxon signed ranks test.

RESULTS

Recordings obtained via ultrasound demonstrated significantly more fetal signal loss than those obtained via the direct mode, particularly in the second stage. The FIGO criteria for fetal signal loss with external ultrasound were not fulfilled during this stage for about half the cases.

CONCLUSION

Intrapartum FHR monitoring via a scalp electrode provides far better quality FHR signals than external ultrasound and deserves a more prominent position in fetal surveillance than it currently has.

Cardiotocography and medicolegal issues

Obstetric litigation is on the increase. A review of litigation cases reveals that the majority of claims relating to the intrapartum period arise because the cardiotocograph- (CTG) was misinterpreted or because inappropriate action was taken in the presence of fetal heart rate abnormalities. Compulsory education and training in the interpretation of CTGs and in best practice are key factors in minimizing the threat of litigation. Newer methods, such as pulse oximetry or fetal electrocardiogram waveform analysis, can act as adjuncts to CTG and help to avoid birth asphyxia and hence litigation.

Multi-channel magnetocardiography for detecting beat morphology variations in fetal arrhythmias

OBJECTIVE

Over the last few years, a number of studies have shown that fetal magnetocardiography (fMCG) is useful in describing fetal cardiac activity. A 55-channel MCG system in Ulm was used to record fetal cardiac activity in 12 pregnant women (with normal fetal heart activity in echocardiography) and in 5 pregnant women in whom the echocardiography showed fetal arrhythmias.

METHOD

The recorded MCG data were treated in order to eliminate the maternal signal and three MCG channels with the best signals were used to emulate a standard electrocardiogram (ECG) recording so that standard MCG analysis could be performed.

RESULTS

The results in assessing fetal electrophysiology, demonstrating its potential, are presented here for two fetuses with recorded supraventricular extrasystoles (SVES) and for one with ventricular extrasystoles (VES). Concerning the SVES, the analysis software OMEGA was able to separate three different beat morphologies. The VES could be detected exactly and have been confirmed by postnatal ECG.

CONCLUSION

The beat morphology and the beat-to-beat variations allow new insights into the electrophysiology of the fetal heart.

Reproducibility and reliability of fetal cardiac time intervals using magnetocardiography

We investigated several factors which may affect the accuracy of fetal cardiac time intervals (CTI) determined in magnetocardiographic (MCG) recordings: observer differences, the number of available recording sites and the type of sensor used in acquisition. In 253 fetal MCG recordings, acquired using different biomagnetometer devices between the 15th and 42nd weeks of gestation, P-wave, QRS complex and T-wave onsets and ends were identified in signal averaged data sets independently by different observers. Using a defined procedure for setting signal events, interobserver reliability was high. Increasing the number of registration sites led to more accurate identification of the events. The differences in wave morphology between magnetometer and gradiometer configurations led to deviations in timing whereas the differences between low and high temperature devices seemed to be primarily due to noise. Signal-to-noise ratio played an important overall role in the accurate determination of CTI and changes in signal amplitude associated with fetal maturation may largely explain the effects of gestational age on reproducibility. As fetal CTI may be of value in the identification of pathologies such as intrauterine growth retardation or fetal cardiac hypertrophy, their reliable estimation will be enhanced by strategies which take these factors into account.

Inter-observer variation in assessment of 845 labour admission tests: comparison between midwives and obstetricians in the clinical setting and two experts

OBJECTIVE

To assess the inter-observer agreement in assessment of the labour admission test between midwives and obstetricians in the clinical setting and two experts in the non-clinical setting, the inter-observer agreement between two experts in the non-clinical setting and to what degree fetal distress in labour could be predicted by the two experts.

DESIGN

Observational study.

SETTING

The maternity unit of Hammerfest Hospital, Norway.

POPULATION

Eight hundred and forty-five high and low risk women.

METHOD

The labour admission test was first assessed by the midwife or obstetrician in the clinical setting, and was later assessed by two experts. The traces were assessed as normal, equivocal or ominous. Weighted kappa (kappaw), proportion of agreement (Pa) and predictive values were calculated.

MAIN OUTCOME MEASURES

Weighted kappa, proportion of agreement, sensitivity, positive predictive value and likelihood ratios.

RESULTS

Inter-observer agreement between Expert 1 and Expert 2: kappaw 0.38 (CI 0.31-0.46), Pa for reactive labour admission test 0.86 (CI 0.83-0.88) and Pa for equivocal/ominous test 0.33 (CI 0.26-0.40). Agreement between Expert 1 and midwives/obstetricians: kappaw 0.25 (CI 0.15-0.36), Pa for reactive labour admission test 0.89 (CI 0.87-0.91) and Pa for equivocal/ominous labour admission test 0.18 (CI 0.11-0.25). Agreement between Expert 2 and midwives/obstetricians: kappaw 0.28 (CI 0.20-0.37), Pa for reactive labour admission test 0.85 (CI 0.82-0.88) and Pa for equivocal/ominous test 0.20 (CI 0.14-0.26). Totally 5.9% of the newborns had fetal distress. At cutoff equivocal test, sensitivity was 0.22 and 0.31 in the two observers. Positive predictive values were 0.13 and 0.11. Likelihood ratio for a positive test was 2.30 and 1.92 and likelihood ratio for a negative test 0.86 and 0.83.

CONCLUSION

A labour admission test is still routine practice in most obstetric units in the Western world when there is little evidence on its benefits. The results from this study may provide some reconsideration for such practice, and for more research.

The combination of computerized cardiotocography and amniotic fluid index for the prediction of neonatal acidemia at birth: a modified biophysical profile

OBJECTIVE

To study the combination of computerized cardiotocography (cCTG) and the amniotic fluid index (AFI) in the prediction of neonatal acidemia at birth.

METHODS

A total of 89 singleton third-trimester high-risk pregnancies delivered by Cesarean section, with an AFI evaluated within 24 h from birth, and an antepartum cCTG performed within 6 h from delivery, were studied. The score was the sum of values for AFI (oligo/anhydramnios = 1, normal = 0) and cCTG (Dawes-Redman criteria, not met = 1, met = 0). The endpoint was to predict an abnormal neonatal outcome as defined by an umbilical artery pH of < or = 7.2.

RESULTS

Fifteen neonates had an umbilical artery pH of < 7.2. The combination of cCTG + AFI score was able to predict pH values (< or = 7.20) with an OR = 2.83 (p < 0.02). The diagnostic accuracy of the combination of cCTG + AFI was as follows: sensitivity 80%, specificity 58%, positive predictive value 28%, negative predictive value 83%.

COMMENT

We suggest that the cCTG + AFI score may be of value in the prediction of neonatal acidemia and help in the management of third-trimester high-risk pregnancies.

Fetal heart rate patterns in normal and ritodrine-treated pregnancies, detected by magnetocardiography

OBJECTIVE

The aim of the present study was to test the validity of magnetocardiography in the diagnosis of fetal heart rate arrhythmias in normal pregnancies, as compared to the number of arrhythmias reported in other series, which were detected by use of other diagnostic techniques. We also evaluated the influence of ritodrine on the fetal heart rhythm in pregnancies treated for the risk of preterm labor by means of magnetocardiography, in order to provide preliminary results that could be utilized in the future establishment of magnetocardiography as a screening procedure in the diagnosis and management of fetal arrhythmias.

METHODS

We performed a prospective study on two subgroups of pregnant women: one of 84 women with normal healthy singleton pregnancies and one of 68 pregnant women treated with ritodrine for the risk of preterm labor.

RESULTS

The prevalence of fetal arrhythmias in the first subgroup was 3.5% (3/84), while in the second subgroup the prevalence was 16% (11/68).

CONCLUSIONS

The incidence of fetal arrhythmias detected in our population of normal pregnancies was comparable to that reported in previous studies by use of other techniques. Results gained from the second subgroup, although not comparable to others, owing to lack of similar reports, led us to believe that magnetocardiography's advantages over conventional methods of fetal cardiac surveillance could highlight the technique as a useful screening procedure for the detection of preterm fetuses, which should be submitted to closer investigation, because of the arrhythmias caused by ritodrine infusion.

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.

Evaluation of fetal heart monitoring in the first stage of labor

OBJECTIVE

To evaluate the usefulness of continuous electronic fetal heart rate (FHR) monitoring in the first stage of labor.

METHODS

A total of 814 pregnant women in labor without identifiable risk factors was divided into two groups. In group A (468 cases), continuous FHR monitoring began in the earliest phase of the first stage of labor (cervical dilatation < or = 4 cm), while in group B (346 cases) it began when the cervical dilatation was > 4 cm. Initial FHR tracings were normal in all 814 cases. The fetal monitoring findings were analyzed at 10-min intervals, and comparisons were made between the two groups concerning FHR findings and their correlation with the state of the newborns.

RESULTS

No significant difference was found between the two groups in the incidence of repetitive variable decelerations (1.9% and 1.7%, respectively); sporadic variable decelerations (9.2% and 8.7%, respectively); persistent repetitive late decelerations that resulted in Cesarean section (1.1% and 1.4%, respectively); or sporadic late decelerations (8.3% and 8.1%, respectively). One newborn from each group required intensive neonatal care.

CONCLUSIONS

The same tracing sufficiency of fetal stress was observed in the two groups. However, the manner of labor supervision in group B seemed to be more beneficial, because of greater maternal comfort, a lower necessity for personnel, lower consumption of cardiotocographic materials and the possibility of labor induction for more women. Since fetal monitoring is widely used, it is preferable to start continuous FHR monitoring when the dilatation of the cervix approximates 4-5 cm (second phase of the first stage of labor) without risk of fetal loss.

Managing nonreassuring fetal heart rate patterns before cesarean delivery. Compliance with ACOG recommendations

OBJECTIVE

To determine the rate of compliance with current American College of Obstetricians and Gynecologists (ACOG) recommendations for management of parturients undergoing cesarean delivery for persistent nonreassuring fetal heart rate (FHR) tracings.

STUDY DESIGN

We performed a retrospective chart review (July 1995-June 1998) of all parturients who underwent cesarean delivery for nonreassuring FHR tracings. Outcome measures included maneuvers for fetal assessment (scalp stimulation or scalp blood pH) and therapeutic interventions (tocolytic agents for reducing uterine activity or amnioinfusion). Patients with multiple gestations and cesarean delivery for other indications were excluded. Student's t test, chi 2 and Fisher's exact tests were used; odds ratio and 95% confidence interval were calculated. P < .05 was considered significant.

RESULTS

Cesarean delivery for persistent nonreassuring FHR patterns included 134 (3.6%) of the 3,671 deliveries during three years. Thirty patients produced intrapartum FHR tracings containing persistent variable decelerations; 12 (40%) of these patients received amnioinfusion. In only 37% (50/134) of cases was there a documented attempt at scalp or acoustic stimulation prior to delivery. Scalp pH was obtained in 15% (15/98) of patients whose cervix was at least 3 cm dilated. Tocolytic agents were used for intrauterine resuscitation in 25% (34/134) of cases; their use varied significantly (P = .006) with the type of FHR abnormality.

CONCLUSION

At our tertiary center, ACOG recommendations for management of nonreassuring intrapartum FHR tracings were used in a limited number of cases.

The development and validation of an algorithm for real-time computerised fetal heart rate monitoring in labour

OBJECTIVE

To develop and validate a computerised algorithm for the interpretation of the characteristics of fetal heart rate monitoring in labour.

DESIGN

Prospective observational study.

SETTING

Labour ward in a tertiary hospital.

SAMPLE

Intrapartum cardiotocograms from 24 pregnancies.

METHODS

A computerised algorithm was developed to assess the fetal heart baseline rate, variability, the number of accelerations and the number of decelerations. Twenty five minute segments of cardiotocograms were interpreted by the algorithm and also by seven expert reviewers independently. The reviewers were unaware of the outcome of labour. The reliability of the characteristics of cardiotocography and the validity of the computerised algorithm were assessed using the intraclass correlation coefficient and weighted kappa statistic for continuous and ordinal variables respectively.

RESULTS

The inter rater reliability of the baseline fetal heart rate and the number and type of decelerations was good (intraclass correlation coefficient 0.93, 0.93 and 0.79, respectively). The reliability of baseline variability (kappa = 0.27) and accelerations (intraclass correlation coefficient = 0.27) was poor. The computerised algorithm had good agreement with the reviewers for the baseline fetal heart rate (intraclass correlation coefficient 0.91 to 0.98) and the number of decelerations (intraclass correlation coefficient 0.82 to 0.91), but was less valid as regards the number of late decelerations (intraclass correlation coefficient 0.68 to 0.85) and the number of accelerations (intraclass correlation coefficient 0.06 to 0.80), and was invalid as regards baseline variability (kappa 0.00 to 0.34).

CONCLUSIONS

The high level of validity of the computerised algorithm for the estimation of the baseline fetal heart rate and the number of decelerations justifies its further technical development.

A comparison of performance by medical and midwifery students in multiprofessional teaching

AIM

At Dundee University, midwifery and medical students are taught obstetrics together in a 2-week intensive course. We set out to test the hypothesis that staff time and effort could be saved by using shared resources in teaching a multidisciplinary group of students to an acceptable level.

METHOD

In order to measure the knowledge gain by two different groups of students, we tested the students before and after a timetabled computer-assisted learning (CAL) session focusing on how to interpret a cardiotocograph (CTG). Also, half of each student group was given extra CTG teaching before the CAL session.

RESULTS

The medical students (n=38) increased their median score from 9 to 17 after the CAL (P<0.001) but the midwifery students (n=13) only increased their median score from 12 to 14 after the CAL (n.s.). However, when given a tutorial and CAL, the post-test scores for both medical and midwifery students were similar and significantly higher than pre-test scores (median score increase from 8.5 to 18 for medical students, P<0.001, n=34, and from 9 to 16 for midwifery students, P<0.01 n=11). There was no significant knowledge gain by the medical students who undertook the additional tutorial.

CONCLUSION

We conclude that shared resources could be used by medical and midwifery students to reach equivalent levels of skill in CTG interpretation. However, in order to achieve equivalence, staff time and effort was wasted as medical students were given unnecessary tuition.

The development and evaluation of a computer-assisted teaching programme for intrapartum fetal monitoring

OBJECTIVE

The development and evaluation of a computer-assisted teaching programme of cardiotocography and acid-base balance.

DESIGN

Randomised controlled trial.

PARTICIPANTS

One hundred and seventeen midwifery and obstetric staff at Derriford Hospital, Plymouth.

METHODS

The obstetricians and midwives were randomly allocated to use the teaching programme, either early or late. The late group (control) used the teaching programme three months after the early group. To assess the effect of the teaching programme, participants were tested on four occasions over eight months by a multiple choice questionnaire. Two questionnaires on ease of use were also completed.

MAIN OUTCOME MEASURES

Multiple choice questionnaire scores and opinion questionnaire results.

RESULTS

The mean score in the early group improved from 50-8% (test 1, pre-teaching programme) to 70.2% (test 2, post-teaching programme). The mean score in the control group was 50.3% (test 1) and 54.8% (test 2). Knowledge was retained up to seven months.

CONCLUSIONS

The teaching programme was effective in improving knowledge of acid-base balance and cardiotocography and can be used by all staff whilst on duty on the labour ward.

Using telemedicine to facilitate training in cardiotocography (CTG) interpretation

Electronic fetal monitoring is a controversial practice in modern obstetric care and is frequently an aspect of medicolegal cases involving the management of labour and delivery. The interpretation of the cardiotocograph (CTG) produced by such monitors is a skill required by those caring for the pregnant woman. Studies have shown that most 'experts' do not interpret CTGs in a consistent manner, when compared with either other experts or themselves. However, it has also been shown that consistency can be improved with training. Telemedicine has been used to advantage in the training of obstetrics and gynaecology registrars in CTG interpretation.

Inconsistencies in classification by experts of cardiotocograms and subsequent clinical decision

Inter-observer agreement in the interpretation according to the FIGO guidelines of 33 cardiotocographic tracings by experts and subsequent clinical decision was evaluated, using the kappa statistic (K) and the proportions of agreement (Pa). Overall agreement in the classification of tracings was fair (K = 0.48) and was better for normal (Pa = 0.62), than for suspicious (Pa = 0.42) or pathologic tracings (Pa = 0.25). Overall agreement on clinical decision was slightly higher (K = 0.59), but mostly was centred on the decision to take 'no action' (Pa = 0.79). Experts especially disagreed over the decisions to 'monitor closely' (Pa = 0.14) or to 'intervene immediately' (Pa = 0.38). These limitations should be taken into account in clinical audits and in medical jurisprudence.

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.