Joeh Judith van Laar

Estimation of internal uterine pressure by joint amplitude and frequency analysis of electrohysterographic signals

Monitoring the uterine contraction provides important prognostic information during pregnancy and parturition. The existing methods employed in clinical practice impose a compromise between reliability and invasiveness. A promising technique for uterine contraction monitoring is electrohysterography (EHG). The EHG signal measures the electrical activity which triggers the contraction of the uterine muscle. In this paper, a non-invasive method for intrauterine pressure (IUP) estimation by EHG signal analysis is proposed. The EHG signal is regarded as a non-stationary signal whose frequency and amplitude characteristics are related to the IUP. After acquisition in a multi-channel configuration, the EHG signal is therefore analyzed in the time-frequency domain. A first estimation of the IUP is then derived by calculation of the unnormalized first statistical moment of the frequency spectrum. The estimation accuracy is finally increased by identification of a second-order polynomial model. The proposed method is compared to root mean squared analysis and optimal linear filtering and validated by simultaneous measurement of the IUP on nine women during labor. The results suggest that the proposed EHG signal analysis provides an accurate estimate of the IUP.

Inter-electrode delay estimators for electrohysterographic propagation analysis

Premature birth is a major cause of mortality and permanent dysfunctions. Several parameters derived from single channel electrohysterographic (EHG) signals have been considered to determine contractions leading to preterm delivery. The results are promising, but improvements are needed. As effective uterine contractions result from a proper action potential propagation, in this paper we focus on the propagation properties of EHG signals, which can be predictive of preterm delivery. Two standard delay estimators, namely maximization of the cross-correlation function and spectral matching, are adapted and implemented for the assessment of inter-electrode delays of propagating EHG signals. The accuracy of the considered standard estimators might be hampered by a poor inter-channel correlation. An improved dedicated approach is therefore proposed. By simultaneous adaptive estimation of the volume conductor transfer function and the delay, a dedicated method is conceived for improving the inter-channel signal similarity during delay calculation. Furthermore, it provides delay estimates without resolution limits and it is suitable for low sampling rates, which are appropriate for EHG recording. The three estimators were evaluated on EHG signals recorded on seven women. The dedicated approach provided more accurate estimates due to a 22% improvement of the initial average inter-channel correlation.

Fetal heart rate variability during pregnancy, obtained from non-invasive electrocardiogram recordings

Non‐invasive spectral analysis of fetal heart rate variability is a promising new field of fetal monitoring. To validate this method properly, we studied the relationship between gestational age and the influence of fetal rest–activity state on spectral estimates of fetal heart rate variability.

On the propagation analysis of electrohysterographic signals

Premature birth is a leading cause of fetal mortality and long-term morbidity. The effective treatment of preterm uterine contractions requires new methods for predicting delivery. The electrohysterographic (EHG) signal is a measure of the bioelectrical process underlying the uterine contraction. The analysis of parameters derived from the EHG signal can therefore provide fundamental information for the prognosis of labor. In this paper, we focus on the propagation of the EHG signal recorded during delivery by multiple electrodes. For the inter-electrode delay assessment and propagation analysis, two different methods are implemented. One is based on the prior estimation of the uterine mechanical activity by EHG signal processing. The delay is then calculated by the cross-correlation function between the mechanical activity estimated at each sensor. The other method is a high temporal resolution adaptive delay estimator that operates directly on EHG signals. The previously demonstrated accuracy of the mechanical estimates and the agreement between the delays provided by the methods confirm the tight relationship between the mechanical and electrical activity of the uterus. However, our results suggest that a higher temporal resolution delay estimator is preferred.

A systematic review of prenatal screening for congenital heart disease by fetal electrocardiography

Congenital heart disease (CHD) is the most common severe congenital anomaly worldwide. Diagnosis early in pregnancy is important, but the detection rate by two‐dimensional ultrasonography is only 65%–81%.

Orientation of the electrical heart axis in mid-term pregnancy.

The unique fetal shunting system causes an increased cardiac muscle mass in the right ventricle [1]. Cardiac currents initiating each contraction are measured from the outside as the electrocardiogram (ECG), the main direction of propagation is referred to as the electrical heart axis. Ventricular depolarization involves the largest cell mass, yielding the largest ECG signal. Therefore, the QRS segment amplitude mainly defines the electrical heart axis. Due to the increased right ventricular mass in fetuses, the electrical heart axis is expected to point toward the right. This has been confirmed in term fetuses during labor and in neonates directly postpartum [2,3]. In contrast, the electrical heart axis of adults points toward the left [4]. However, it is well-known that in both adults and newborns the orientation of the electrical heart axis can vary widely from person to person [2]. For term fetuses during labor, the orientation of the electrical heart axis has been described by Larks et al. in the 1960s [3]. Their recording techniques are outdated, and they did not take the fetal orientation into account. Despite these shortcomings, they already acknowledged the possibilities of the electrical heart axis to contribute in distinguishing between normal intra-uterine development, congenital heart disease and fetal distress. The orientation of the fetal electrical heart axis during gestation has never been described. The relevance of the electrical heart axis increased, since fetal ECG is used to study fetal well-being more often. The aim of this study is to determine the direction of the fetal electrical heart axis in mid-term pregnancy.

Effect of tocolytic drugs on fetal heart rate variability: a systematic review

Abstract Introduction: Tocolytics may cause changes in fetal heart rate (HR) pattern, while fetal heart rate variability (HRV) is an important marker of fetal well-being. We aim to systematically review the literature on how tocolytic drugs affect fetal HRV. Materials and methods: We searched CENTRAL, PubMed and EMBASE up to June 2016. Studies published in English, using computerized or visual analysis to describe the effect of tocolytics on HRV in human fetuses were included. Studies describing tocolytics during labor, external cephalic version, pre-eclampsia and infection were excluded. Eventually, we included six studies, describing 169 pregnant women. Results: Nifedipine, atosiban and indomethacin administration show no clinically important effect on fetal HRV. Following administration of magnesium sulfate decreased variability and cases of bradycardia are described. Fenoterol administration results in a slight increase in fetal HR with no changes in variability. After ritodrine administration increased fetal HR and decreased variability is seen. The effect of co-administration of corticosteroids should be taken into account. Conclusion: In order to prevent iatrogenic preterm labor, the effects of tocolytic drugs on fetal HRV should be taken into account when monitoring these fetuses.

Ultrasound transducer positioning aid for fetal heart rate monitoring

Fetal heart rate (fHR) monitoring is usually performed by Doppler ultrasound (US) techniques. For reliable fHR measurements it is required that the fetal heart is located within the US beam. In clinical practice, clinicians palpate the maternal abdomen to identify the fetal presentation and then the US transducer is fixated on the maternal abdomen where the best fHR signal can be obtained. Finding the optimal transducer position is done by listening to the strength of the Doppler audio output and relying on a signal quality indicator of the cardiotocographic (CTG) measurement system. Due to displacement of the US transducer or displacement of the fetal heart out of the US beam, the fHR signal may be lost. Therefore, it is often necessary that the obstetrician repeats the tedious procedure of US transducer positioning to avoid long periods of fHR signal loss. An intuitive US transducer positioning aid would be highly desirable to increase the work flow for the clinical staff. In this paper, the possibility to determine the fetal heart location with respect to the transducer by exploiting the received signal power in the transducer elements is shown. A commercially available US transducer used for fHR monitoring is connected to an US open platform, which allows individual driving of the elements and raw US data acquisition. Based on the power of the received Doppler signals in the transducer elements, the fetal heart location can be estimated. A beating fetal heart setup was designed and realized for validation. The experimental results show the feasibility of estimating the fetal heart location with the proposed method. This can be used to support clinicians in finding the optimal transducer position for fHR monitoring more easily.