Sensors for Fetal Hypoxia and Metabolic Acidosis: A Review

Fetal monitoring technologies for the detection of intrapartum hypoxia - challenges and opportunities

Intrapartum fetal hypoxia is related to long-term morbidity and mortality of the fetus and the mother. Fetal surveillance is extremely important to minimize the adverse outcomes arising from fetal hypoxia during labour. Several methods have been used in current clinical practice to monitor fetal well-being. For instance, biophysical technologies including cardiotocography, ST-analysis adjunct to cardiotocography, and Doppler ultrasound are used for intrapartum fetal monitoring. However, these technologies result in a high false-positive rate and increased obstetric interventions during labour. Alternatively, biochemical-based technologies including fetal scalp blood sampling and fetal pulse oximetry are used to identify metabolic acidosis and oxygen deprivation resulting from fetal hypoxia. These technologies neither improve clinical outcomes nor reduce unnecessary interventions during labour. Also, there is a need to link the physiological changes during fetal hypoxia to fetal monitoring technologies. The objective of this article is to assess the clinical background of fetal hypoxia and to review existing monitoring technologies for the detection and monitoring of fetal hypoxia. A comprehensive review has been made to predict fetal hypoxia using computational and machine-learning algorithms. The detection of more specific biomarkers or new sensing technologies is also reviewed which may help in the enhancement of the reliability of continuous fetal monitoring and may result in the accurate detection of intrapartum fetal hypoxia.

Current Innovative Methods of Fetal pH Monitoring—A Brief Review

In this study, we explore the “why?”, and “how?”, monitoring the pH of the fetal scalp is used, and show its limitations. In addition, we review the development of new devices based on the modern physics and nanomaterials serving this topic. Most of the works we found in our search have focused on improving the prognostic of fetal heart rate monitoring, because it is the “golden standard” in determining fetal distress. Although the best-known screening method, it can only provide limited information about the actual status of the fetus. The best predictive assessment, with the highest reproducibility, states that a normal fetal heart rate is indicative of a healthy baby. However, its excellent sensitivity is much reduced when identifying the actual “distress”. This is when second-line monitoring methods come into play to guide the diagnostics and direct the obstetrician towards an action plan. Although a historic method, fetal scalp pH sampling is still under review as to its efficiency and place in the current obstetrics. Continuous surveillance of the fetal parameters is important, especially for the fetuses undergoing intrauterine growth restricted (IUGR). Since fetal scalp blood sampling is still under research and is a randomized controlled trial, which compares the relevance of pH and lactates to the obstetrical situation, the maternal-fetal medicine could greatly benefit from the introduction of engineered nanomedicines to the field.

What Is Left for Real-Life Lactate Monitoring? Current Advances in Electrochemical Lactate (Bio)Sensors for Agrifood and Biomedical Applications

Monitoring of lactate is spreading from the evident clinical environment, where its role as a biomarker is notorious, to the agrifood ambit as well. In the former, lactate concentration can serve as a useful indicator of several diseases (e.g., tumour development and lactic acidosis) and a relevant value in sports performance for athletes, among others. In the latter, the spotlight is placed on the food control, bringing to the table meaningful information such as decaying product detection and stress monitoring of species. No matter what purpose is involved, electrochemical (bio)sensors stand as a solid and suitable choice. However, for the time being, this statement seems to be true only for discrete measurements. The reality exposes that real and continuous lactate monitoring is still a troublesome goal. In this review, a critical overview of electrochemical lactate (bio)sensors for clinical and agrifood situations is performed. Additionally, the transduction possibilities and different sensor designs approaches are also discussed. The main aim is to reflect the current state of the art and to indicate relevant advances (and bottlenecks) to keep in mind for further development and the final achievement of this highly worthy objective.

Fetal Wellbeing Monitoring – A Review Article

While assessing maternal health is relatively easy, assessing fetal well-being has always been tricky. This has led to tremendous technological development in fetal well-being assessment, thus bridging the gap between biotechnology and antenatal medicine. It is broadly divided into early pregnancy, late pregnancy, and during labour assessment. While the early assessment involves genetic check-ups and malformations, the late pregnancy check-ups aim at delivering a healthy fetus at term by normal vaginal delivery. The early tests can be invasive or non-invasive. Non-invasive include cell-free fetal DNA assessment and fetal cell-based assessment. Invasive tests include amniocentesis and chorionic villous sampling. These are followed by chromosomal microarray and next-generation sequencing. Under this procedure, exome sequencing is done, which is either clinical or whole. Sequencing of the whole genome can also be done. A recent advancement is pre-implantation genetic testing. These are mainly useful in identifying monogenic disorders for which the locus causing disease is identified beyond any doubt. In late pregnancy, the most commonly used test is biophysical. It works on the principle that an increase in the fetal heart rate occurs in conjugation with fetal movements. The next widely employed technology is Doppler, which is used to know fetal heart rates, valve timing intervals, and umbilical artery waveforms. Cardiotocography is also widely used both during pregnancy and during labour. It measures the fetal heart rate while correlating it with uterine contractions. Wireless fetal and maternal heart monitoring and telemonitoring are recent upcoming fields.

[Comparison of the measurement of lactate at the cord by hand-held devices approved for use during labor with a reference device]

OBJECTIVE

To compare two portable lactate devices, Lactate Scout and StatStrip Xpress, to a laboratory reference device by assessing the concordance of cord blood lactate values at birth.

METHODS

We conducted a single-center prospective validation study in a level 3 maternity hospital. For all cord samples taken at birth, we analyzed lactates on the reference device (GEM4000®) and on two portable devices Lactate Scout and StatStrip Xpress. We compared the lactate values from each of the two handheld devices to the reference device.

RESULTS

A total of 101 samples were collected. Each was analyzed by all three machines. The average lactate value obtained by the different machines was 3.7mmol/L. The mean difference between the Lactate Scout and GEM4000® apparatus was 0.0mmol/L±0.8mmol/L. Between these two devices at lactate threshold of 4.8mmol/L, the negative predictive value was 96,2% (76/79) and the area under the curve was 0.98 (95% CI 0.96-1]. The mean difference between StatStrip Xpress and GEM4000® was 0.1mmol/L±0.7mmol/L. Between these two devices at the lactate threshold of 4.8mmol/L, the negative predictive value was 97,4% (76/78) and the area under the curve was 0.95 (95% CI 0.86-1).

CONCLUSION

There is a good correlation between the lactates obtained by the reference device and the two portable devices Lactate Scout and StatStrip Xpress.

A Review on Magnetic Induction Spectroscopy Potential for Fetal Acidosis Examination

Fetal acidosis is one of the main concerns during labor. Currently, fetal blood sampling (FBS) has become the most accurate measurement of acidosis detection. However, it is invasive and does not provide a real time measurement due to laboratory procedures. Delays in diagnosis of acidosis have caused serious injury to the fetus, especially for the brain and the heart. This paper reviews the new technique in diagnosis of acidosis non-invasively. Magnetic Induction Spectroscopy (MIS) has been proposed to be a new device for acidosis detection in recent years. This paper explains the basic principle of MIS and outlines the design specifications and design considerations for a MIS pH probe. It is expected that readers will gain a basic understanding of the development of a MIS pH probe from this review.

Relationship Between Deceleration Morphology and Phase Rectified Signal Averaging-Based Parameters During Labor

During labor, uterine contractions trigger the response of the autonomic nervous system (ANS) of the fetus, producing sawtooth-like decelerations in the fetal heart rate (FHR) series. Under chronic hypoxia, ANS is known to regulate FHR differently with respect to healthy fetuses. In this study, we hypothesized that such different ANS regulation might also lead to a change in the FHR deceleration morphology. The hypothesis was tested in an animal model comprising nine normoxic and five chronically hypoxic fetuses that underwent a protocol of umbilical cord occlusions (UCOs). Deceleration morphologies in the fetal inter-beat time interval (FRR) series were modeled using a trapezoid with four parameters, i.e., baseline b, deceleration depth a, UCO response time τ u and recovery time τ r . Comparing normoxic and hypoxic sheep, we found a clear difference for τ u (24.8±9.4 vs. 39.8±9.7 s; p < 0.05), a (268.1±109.5 vs. 373.0±46.0 ms; p < 0.1) and Δτ = τ u - τ r (13.2±6.9 vs. 23.9±7.5 s; p < 0.05). Therefore, the animal model supported the hypothesis that hypoxic fetuses have a longer response time τ u and larger asymmetry Δτ as a response to UCOs. Assessing these morphological parameters during labor is challenging due to non-stationarity, phase desynchronization and noise. For this reason, in the second part of the study, we quantified whether acceleration capacity (AC), deceleration capacity (DC), and deceleration reserve (DR), computed through Phase-Rectified Signal Averaging (PRSA, known to be robust to noise), were correlated with the morphological parameters. DC, AC and DR were correlated with τ u , τ r and Δτ for a wide range of the PRSA parameter T (Pearson's correlation ρ > 0.8, p < 0.05). In conclusion, deceleration morphologies have been found to differ between normoxic and hypoxic sheep fetuses during UCOs. The same difference can be assessed through PRSA based parameters, further motivating future investigations on the translational potential of this methodology on human data.

Umbilical cord lactate compared with pH as predictors of intrapartum asphyxia

Despite advances in fetal monitoring during labor, one of the most critical causes of neonatal death and neurologic injuries remains intrapartum asphyxia. Umbilical cord gases can be used to detect acidosis and fetal distress. We conducted a retrospective, multicenter study to evaluate umbilical cord blood pH and lactate as a mean of evaluating the degree of intrapartum hypoxia and also to establish which of the two is more reliable in predicting morbidity in term neonates. The present study utilized a total of 124 cases that met the criteria for intrapartum asphyxia and 150 normal term newborns that were randomly selected as case control. Both umbilical cord lactate and pH proved to be accurate predictors of neonatal morbidity caused by intrapartum hypoxia. Lactate proved to be superior to pH in predicting adverse neonatal outcome. The greatest sensibility and specificity in predicting intrapartum asphyxia were achieved in our study by using a cutoff value of 3.75 mmol/l for lactate and 7.24 for pH.

Machine Learning-Assisted Raman Spectroscopy for pH and Lactate Sensing in Body Fluids

This study presents the combination of Raman spectroscopy with machine learning algorithms as a prospective diagnostic tool capable of detecting and monitoring relevant variations of pH and lactate as recognized biomarkers of several pathologies. The applicability of the method proposed here is tested both in vitro and ex vivo. In a first step, Raman spectra of aqueous solutions are evaluated for the identification of characteristic patterns resulting from changes in pH or in the concentration of lactate. The method is further validated with blood and plasma samples. Principal component analysis is used to highlight the relevant features that differentiate the Raman spectra regarding their pH and concentration of lactate. Partial least squares regression models are developed to capture and model the spectral variability of the Raman spectra. The performance of these predictive regression models is demonstrated by clinically accurate predictions of pH and lactate from unknown samples in the physiologically relevant range. These results prove the potential of our method to develop a noninvasive technology, based on Raman spectroscopy, for continuous monitoring of pH and lactate in vivo.

A new microdialysis probe for continuous lactate measurement during fetal monitoring: Proof of concept in an animal model

INTRODUCTION

Cardiotocography (CTG) is currently the most commonly used method for intrapartum fetal monitoring during labor. However, a high false-positive rate of fetal acidosis indicated by CTG leads to an increase in obstetric interventions. We developed a microdialysis probe that is integrated into a fetal scalp electrode allowing continuous measurement of lactate subcutaneously, thus giving instant information about the oxygenation status of the fetus. Our aim was to establish proof of concept in an animal model using a microdialysis probe to monitor lactate subcutaneously.

MATERIAL AND METHODS

We performed an in vivo study in adult male wild-type Wistar rats. We modified electrodes used for CTG monitoring in human fetuses to incorporate a microdialysis membrane. Optimum flow rates for microdialysis were determined in vitro. For the in vivo experiment, a microdialysis probe was inserted into the skin on the back of the animal. De-oxygenation and acidosis were induced by lowering the inspiratory oxygen pressure. Oxygenation and heart rate were monitored. A jugular vein cannula was inserted to draw blood samples for analysis of lactate, pH, pco2 , and saturation. Lactate levels in dialysate were compared with plasma lactate levels.

RESULTS

Baseline blood lactate levels were around 1 mmol/L. Upon de-oxygenation, oxygen saturation fell to below 40% for 1 h and blood lactate levels increased 2.5-fold. Correlation of dialysate lactate levels with plasma lactate levels was 0.89 resulting in an R2 of .78 in the corresponding linear regression.

CONCLUSIONS

In this animal model, lactate levels in subcutaneous fluid collected by microdialysis closely reflected blood lactate levels upon transient de-oxygenation, indicating that our device is suitable for subcutaneous measurement of lactate. Microdialysis probe technology allows the measurement of multiple compounds in the dialysate, such as glucose, albumin, or inflammatory mediators, so this technique may offer the unique possibility to shed light on fetal physiology during the intrapartum period.

Determination of physiological lactate and pH by Raman spectroscopy

Lactate and pH values in human blood are important physiological parameters that can reflect serious pathological states as sepsis or hypoxia. In this study we demonstrate that we can determine lactate and pH values from blood samples by Raman spectroscopy combined with multivariate analysis at medically relevant resolution and reliability. The method prepares the base for new real-time in vivo analytics for a number of pathological cases and physiological control in competitive sports. We demonstrate the capability to resolve pH variations of 0.04 and lactate concentrations of 0.20 mM ex vivo.

Environmental Contaminants Exposure and Preterm Birth: A Systematic Review

Preterm birth is an obstetric condition associated with a high risk of infant mortality and morbidities in both the neonatal period and later in life, which has also a significant public health impact because it carries an important societal economic burden. As in many cases the etiology is unknown, it is important to identify environmental factors that may be involved in the occurrence of this condition. In this review, we report all the studies published in PubMed and Scopus databases from January 1992 to January 2019, accessible as full-text articles, written in English, including clinical studies, original studies, and reviews. We excluded articles not written in English, duplicates, considering inappropriate populations and/or exposures or irrelevant outcomes and patients with known risk factors for preterm birth (PTB). The aim of this article is to identify and summarize the studies that examine environmental toxicants exposure associated with preterm birth. This knowledge will strengthen the possibility to develop strategies to reduce the exposure to these toxicants and apply clinical measures for preterm birth prevention.