Dedicated Entropy Measures for Early Assessment of Pregnancy Progression From Single-Channel Electrohysterography.

OBJECTIVE: Preterm birth is a large-scale clinical problem involving over 10% of infants. Diagnostic means for timely risk assessment are lacking and the underlying physiological mechanisms unclear. To improve the evaluation of pregnancy before term, we introduce dedicated entropy measures derived from a single-channel electrohysterogram (EHG). METHODS: The estimation of approximate entropy (ApEn) and sample entropy (SampEn) is adjusted to monitor variations in the regularity of single-channel EHG recordings, reflecting myoelectrical changes due to pregnancy progression. In particular, modifications in the tolerance metrics are introduced for improving robustness to EHG amplitude fluctuations. An extensive database of 58 EHG recordings with 4 monopolar channels in women presenting with preterm contractions was manually annotated and used for validation. The methods were tested for their ability to recognize the onset of labor and the risk of preterm birth. Comparison with the best single-channel methods according to the literature was performed. RESULTS: The reference methods were outperformed. SampEn and ApEn produced the best prediction of delivery, although only one channel showed a significant difference () between labor and nonlabor. The modified ApEn produced the best prediction of preterm delivery, showing statistical significance () in three channels. These results were also confirmed by the area under the receiver operating characteristic curve and fivefold cross validation. CONCLUSION: The use of dedicated entropy estimators improves the diagnostic value of EHG analysis earlier in pregnancy. SIGNIFICANCE: Our results suggest that changes in the EHG might manifest early in pregnancy, providing relevant prognostic opportunities for pregnancy monitoring by a practical single-channel solution.

The electrical heart axis and ST events in fetal monitoring: A post-hoc analysis following a multicentre randomised controlled trial.

OBJECTIVE: Reducing perinatal morbidity and mortality is one of the major challenges in modern health care. Analysing the ST segment of the fetal electrocardiogram was thought to be the breakthrough in fetal monitoring during labour. However, its implementation in clinical practice yields many false alarms and ST monitoring is highly dependent on cardiotocogram assessment, limiting its value for the prediction of fetal distress during labour. This study aims to evaluate the relation between physiological variations in the orientation of the fetal electrical heart axis and the occurrence of ST events. METHODS: A post-hoc analysis was performed following a multicentre randomised controlled trial, including 1097 patients from two participating centres. All women were monitored with ST analysis during labour. Cases of fetal metabolic acidosis, poor signal quality, missing blood gas analysis, and congenital heart disease were excluded. The orientation of the fetal electrical heart axis affects the height of the initial T/QRS baseline, and therefore the incidence of ST events. We grouped tracings with the same initial baseline T/QRS value. We depicted the number of ST events as a function of the initial baseline T/QRS value with a linear regression model. RESULTS: A significant increment of ST events was observed with increasing height of the initial T/QRS baseline, irrespective of the fetal condition; correlation coefficient 0.63, p<0.001. The most frequent T/QRS baseline is 0.12. CONCLUSION: The orientation of the fetal electrical heart axis and accordingly the height of the initial T/QRS baseline should be taken into account in fetal monitoring with ST analysis.

Tocogram characteristics of uterine rupture: a systematic review.

PURPOSE: Timely diagnosing a uterine rupture is challenging. Based on the pathophysiology of complete uterine wall separation, changes in uterine activity are expected. The primary objective is to identify tocogram characteristics associated with uterine rupture during trial of labor after cesarean section. The secondary objective is to compare the external tocodynamometer with intrauterine pressure catheters. METHODS: MEDLINE, EMBASE, and the Cochrane library were systematically searched for eligible records. Moreover, clinical guidelines were screened. Studies analyzing tocogram characteristics of uterine rupture during trial of labor after cesarean section were appraised and included by two independent reviewers. Due to heterogeneity, a meta-analysis was only feasible for uterine hyperstimulation. RESULTS: Thirteen studies were included. Three tocogram characteristics were associated with uterine rupture. (1) Hyperstimulation was more frequently observed compared with controls during the delivery (38 versus 21 % and 58 versus 53 %), and in the last 2 h prior to birth (19 versus 4 %). Results of meta-analysis: OR 1.68 (95 % CI 0.97-2.89), p = 0.06. (2) Decrease of uterine activity was observed in 14-40 % and (3) an increasing baseline in 10-20 %. Five studies documented no changes in uterine activity or Montevideo units. A direct comparison between external tocodynamometer and intrauterine pressure catheters was not feasible. CONCLUSIONS: Uterine rupture can be preceded or accompanied by several types of changes in uterine contractility, including hyperstimulation, reduced number of contractions, and increased or reduced baseline of the uterine tonus. While no typical pattern has been repeatedly reported, close follow-up of uterine contractility is advised and hyperstimulation should be prevented.

Toward a new modality for detecting a uterine rupture: electrohysterogram propagation analysis during trial of labor after cesarean.

OBJECTIVE: Observational cohort study which aimed to explore the potential of electrohysterogram (EHG) analysis for detecting a uterine rupture during trial of labor after cesarean. The EHG propagation characteristics surrounding the uterine scar of six patients with a previous cesarean section were compared to a control group of five patients without a scarred uterus. METHODS: The EHG was recorded during the first stage of labor using a high-resolution 64-channel electrode grid positioned on the maternal abdomen across the cesarean scar. Based on simulations, the inter-channel correlation and propagation direction were adopted as EHG parameters for evaluating possible disruption of electrical propagation by the uterine scar. RESULTS: No significant differences in inter-channel correlation or propagation direction were observed between the group of patients with an intact uterine scar and the control group. A strong predominance of vertical propagation was observed in one case, in which scar rupture occurred. CONCLUSIONS: The results support unaffected propagation of electrical activity through the intact uterine scar tissue suggesting that changes in the EHG might only occur in case of rupture.

[Electrohysterography. A promising alternative for monitoring contractions]. / Elektrohysterografie. Een veelbelovend alternatief voor weeënregistratie.

Monitoring contractions during labour using the external tocodynamometer can be difficult or even impossible, and using the invasive intrauterine pressure catheter is associated with rare but serious complications. A new non-invasive technique is currently available: electrohysterography (EHG). This technique converts the electrical activity of the uterine muscle into a legible tocogram. The EHG signal has a high correlation with the intra-uterine pressure and provides a more accurate assessment of uterine activity compared to external tocodynamometry. EHG is suitable for women in labour with failure of the external tocodynamometer. In clinical practice EHG also appeared to report a more detailed tocographic waveform, like hypertonia or unorganized electrical uterine activity. However, its signal quality depends on adequate skin preparation and correct positioning of the electrodes on the maternal abdomen. Hence, with electrohysterography as non-invasive alternative for uterine monitoring, choosing between safety and accuracy is no longer necessary.

Study protocol: PoPE-Prediction of Preterm delivery by Electrohysterography.

BACKGROUND: Traditional methods used for prediction of preterm delivery are subjective and inaccurate. The Electrohysterogram (EHG) and in particular the estimation of the EHG conduction velocity, is a relatively new promising method for detecting imminent preterm delivery. To date the analysis of the conduction velocity has relied on visual inspection of the signals. As a next step towards the introduction of EHG analysis as a clinical tool, we propose an automated method for EHG conduction velocity estimation for both the speed and direction of single spike propagation. METHODS/DESIGN: The study design will be an observational cohort study. 100 pregnant women, gestational age between 23 + 5 and 34 weeks, admitted for threatening preterm labor or preterm prelabor rupture of membranes, will be included. The length of the cervical canal will be measured by transvaginal ultrasound. The EHG will be recorded using 4 electrodes in a fixed configuration. Contractions will be detected by analysis of the EHG and using an estimation of the intra uterine pressure. In the selected contractions, the delays between channels will be estimated by cross-correlation, and subsequently, the average EHG conduction velocity will be derived. Patients will be classified as labor group and non-labor group based on the time between measurement and delivery. The average conduction velocity and cervical length will be compared between the groups. The main study endpoints will be sensitivity, specificity, and area under the ROC curve for delivery within 1,2,4,7, and 14 days from the measurement. DISCUSSION: In this study, the diagnostic accuracy of EHG conduction velocity analysis will be evaluated for detecting preterm labor. Visual and automatic detection of contractions will be compared. Planar wave propagation will be assumed for the calculation of the CV vector. TRIAL REGISTRATION: Current Controlled Trials ISRCTN07603227.

Towards improving uterine electrical activity modeling and electrohysterography: ultrasonic quantification of uterine movements during labor.

The electrohysterogram is a potential new tool for diagnosing preterm labor. Parameters from the electrohysterogram may be influenced by uterine movement. An observational study was performed quantifying uterine movement during labor as a step towards improving electrohysterogram analysis for predicting preterm labor. The uterine wall was continuously tracked by ultrasound imaging during first stage of labor while an accelerometer recorded external abdominal accelerations in six women. A cyclic cranial-caudal movement of the uterine wall, caused by maternal respiration, was observed. This is reported and quantified for the first time. Average frequency, amplitude, and peak speed were 0.27 ± 0.07 Hz, 0.68 ± 0.84 cm, and 1.04 ± 1.20 cm/s, respectively. The accelerometer signal correlated with uterine movement and therefore can possibly provide a reference for removing movement-induced artifacts. There is a need to model and measure the effect of uterine movement on the electrohysterogram parameters and make measurements more robust to movement artifacts.

Ultrasound analysis of the uterine wall movement for improved electrohysterographic measurement and modeling.

During pregnancy, analysis of the electrohysterogram (EHG), which measures the uterine electrical activity, can provide a fundamental contribution for the assessment of uterine contractions and the diagnosis of preterm labor. However, several aspects concerning uterine physiology and its link with EHG measurements are still unclear. As a consequence, the EHG is not yet part of the clinical practice. There is general consensus that modeling and analysis of the EHG can be improved only by understanding and integrating the main properties of the uterine physiology at different levels, e:g:, cellular, tissue, and organ, and of different nature, e:g:, electrical, mechanical, and structural. In this study, we use transabdominal ultrasound (US) measurements to investigate the mechanical changes that the uterus undergoes during pregnancy under the effect of contractions. We refer to this measurement as mechanohysterogram. Analysis of the mechanohysterogram highlights, for the first time, two phenomena that can influence EHG signal interpretation, namely, changes in uterine wall thickness during contractions and respiration-induced uterine wall movements. Our results suggest that these phenomena can affect the interpretation of the EHG and should therefore be taken into account for accurate modeling and assessment of the uterine electrical activity.

[Group counselling for the second trimester ultrasound: can group counselling be an alternative for individual counselling?]. / Counseling bij het structureel echoscopisch onderzoek: is groepscounseling een alternatief voor individuele counseling?

OBJECTIVE: To compare group counselling to individual counselling with respect to the second trimester ultrasound. DESIGN: A prospective cohort study at two hospitals. METHOD: At one hospital, 100 pregnant women were counselled on the risks and benefits of the second trimester ultrasound in groups of up to 15 patients. Shortly before the ultrasound they were asked to fill out a questionnaire. Results were compared to 100 women who were counselled individually at another hospital. The primary outcome was the level of informed choice whether or not to undergo the ultrasound, defined as sufficient knowledge and a value-consistent decision. The secondary outcome measures were level of understanding of the second trimester ultrasound and the degree of satisfaction with the counselling. RESULTS: The resulting level of informed choice was 87.0% after group counselling compared to 79.4% after individual counselling (p = 0.47). The mean knowledge score was 8.8 for the women who attended group counselling; women who were individually counselled had a mean score of 7.4 (p < 0.001). Satisfaction with counselling was 7.0 for group counselling and 6.2 for individual counselling (p < 0.001). CONCLUSION: Although there was no statistically significant difference in the level of informed choice, group counselling was associated with higher post-counselling knowledge and satisfaction scores. Group counselling should therefore be considered as an alternative counselling method.

Automated conduction velocity analysis in the electrohysterogram for prediction of imminent delivery: a preliminary study.

BACKGROUND: Analysis of the electrohysterogram (EHG) is a promising diagnostic tool for preterm delivery. For the introduction in the clinical practice, analysis of the EHG should be reliable and automated to guarantee reproducibility. STUDY GOAL: Investigating the feasibility of automated analysis of the EHG conduction velocity (CV) for detecting imminent delivery. MATERIALS AND METHODS: Twenty-two patients presenting with uterine contractions (7 preterm) were included. An EHG was obtained noninvasively using a 64-channel high-density electrode grid. Contractions were selected based on the estimated intrauterine pressure derived from the EHG, the tocodynamometer, and maternal perception. Within the selected contractions, the CV vector was identified in two dimensions. RESULTS: Nine patients delivered within 24 hours and were classified as a labor group. 64 contractions were analyzed; the average amplitude of the CV vector was significantly higher for the labor group, 8.65 cm/s ± 1.90, compared to the nonlabor group, 5.30 cm/s ± 1.47 (P < 0.01). CONCLUSION: The amplitude of the CV is a promising parameter for predicting imminent (preterm) delivery. Automated estimation of this parameter from the EHG signal is feasible and should be regarded as an important prerequisite for future clinical studies and applications.

Risk of uterine rupture in women undergoing trial of labour with a history of both a caesarean section and a vaginal delivery.

PURPOSE: To determine the risk of uterine rupture for women undergoing trial of labour (TOL) with both a prior caesarean section (CS) and a vaginal delivery. METHODS: A systematic literature search was performed using keywords for CS and uterine rupture. The results were critically appraised and the data from relevant and valid articles were extracted. Odds ratios were calculated and a pooled estimate was determined using the Mantel-Haenszel method. RESULTS: Five studies were used for final analysis. Three studies showed a significant risk reduction for women with both a previous CS and a prior vaginal delivery (PVD) compared to women with a previous CS only, and two studies showed a trend towards risk reduction. The absolute risk of uterine rupture with a prior vaginal delivery varied from 0.17 to 0.46%. The overall odds ratio for PVD was 0.39 (95% CI 0.29-0.52, P < 0.00001). CONCLUSION: Women with a history of both a CS and vaginal delivery are at decreased risk of uterine rupture when undergoing TOL compared with women who have only had a CS.