Fetal Pulse Oximetry Research Articles

Sensitivity analysis of transabdominal fetal pulse oximetry using MRI-based simulations.

Transabdominal fetal pulse oximetry offers a promising approach to improve fetal monitoring and reduce unnecessary interventions. Utilizing realistic 3D geometries derived from MRI scans of pregnant women, we conducted photon simulations to determine optimal source-detector configurations for detecting fetal heart rate and oxygenation. Our findings demonstrate the theoretical feasibility of measuring fetal signals at depths up to 30 mm using source-detector (SD) distances greater than 100 mm and wavelengths between 730 and 850 nm. Furthermore, we highlight the importance of customizing SD configurations based on fetal position and maternal anatomy. These insights pave the way for enhanced non-invasive fetal monitoring in clinical application.

Association between intrapartum fetal pulse oximetry and adverse perinatal and long-term outcomes: a systematic review and meta-analysis protocol.

Current methods of intrapartum fetal monitoring based on heart rate, increase the rates of operative delivery but do not prevent or accurately detect fetal hypoxic brain injury. There is a need for more accurate methods of intrapartum fetal surveillance that will decrease the incidence of adverse perinatal and long-term neurodevelopmental outcomes while maintaining the lowest possible rate of obstetric intervention. Fetal pulse oximetry (FPO) is a technology that may contribute to improved intrapartum fetal wellbeing evaluation by providing a non-invasive measurement of fetal oxygenation status. This systematic review and meta-analysis aims to synthesise the evidence examining the association between intrapartum fetal oxygen saturation levels and adverse perinatal and long-term outcomes in the offspring. We will include randomised control trials (RCTs), cohort, cross-sectional and case-control studies which examine the use of FPO during labour as a means of measuring intrapartum fetal oxygen saturation and assess its effectiveness at detecting adverse perinatal and long-term outcomes compared to existing intrapartum surveillance methods. A detailed systematic search of PubMed, EMBASE, CINAHL, The Cochrane Library, Web of Science, ClinicalTrials.Gov and WHO ICTRP will be conducted following a detailed search strategy until February 2024. Three authors will independently review titles, abstracts and full text of articles. Two reviewers will independently extract data using a pre-defined data extraction form and assess the quality of included studies using the Risk of Bias tool for RCTs and Newcastle-Ottawa Scale for observational studies. The grading of recommendations, assessment, development, and evaluation (GRADE) approach will be used to evaluate the certainty of the evidence. We will use random-effects meta-analysis for each exposure-outcome association to calculate pooled estimates using the generic variance method. This systematic review will follow the Preferred Reporting Items for Systematic reviews and Meta-analyses and MOOSE guidelines. CRD42023457368 (04/09/2023).

Recovering fetal signals transabdominally through interferometric near-infrared spectroscopy (iNIRS).

Noninvasive transabdominal fetal pulse oximetry can provide clinicians critical assessment of fetal health and potentially contribute to improved management of childbirth. Conventional pulse oximetry through continuous wave (CW) light has challenges measuring the signals from deep tissue and separating the weak fetal signal from the strong maternal signal. Here, we propose a new approach for transabdominal fetal pulse oximetry through interferometric near-infrared spectroscopy (iNIRS). This approach provides pathlengths of photons traversing the tissue, which facilitates the extraction of fetal signals by rejecting the very strong maternal signal from superficial layers. We use a multimode fiber combined with a mode-field converter at the detection arm to boost the signal of iNIRS. Together, we can detect signals from deep tissue (>∼1.6 cm in sheep abdomen and in human forearm) at merely 1.1 cm distance from the source. Using a pregnant sheep model, we experimentally measured and extracted the fetal heartbeat signals originating from deep tissue. This validated a key step towards transabdominal fetal pulse oximetry through iNIRS and set a foundation for further development of this method to measure the fetal oxygen saturation.

Association between intrapartum fetal pulse oximetry and adverse perinatal and long-term outcomes: a systematic review and meta-analysis protocol

Background: Current methods of intrapartum fetal monitoring based on heart rate, increase the rates of operative delivery but do not prevent or accurately detect fetal hypoxic brain injury. There is a need for more accurate methods of intrapartum fetal surveillance that will decrease the incidence of adverse perinatal and long-term neurodevelopmental outcomes while maintaining the lowest possible rate of obstetric intervention. Fetal pulse oximetry (FPO) is a technology that may contribute to improved intrapartum fetal wellbeing evaluation by providing a non-invasive measurement of fetal oxygenation status. Objective: This systematic review and meta-analysis aims to synthesise the evidence examining the association between intrapartum fetal oxygen saturation levels and adverse perinatal and long-term outcomes in the offspring. Methods: We will include randomised control trials (RCTs), cohort, cross-sectional and case-control studies which examine the use of FPO during labour as a means of measuring intrapartum fetal oxygen saturation and assess its effectiveness at detecting adverse perinatal and long-term outcomes compared to existing intrapartum surveillance methods. A detailed systematic search of PubMed, EMBASE, CINAHL, The Cochrane Library and Web of Science will be conducted following a detailed search strategy until August 2023. Three authors will independently review titles, abstracts and full text of articles. Two reviewers will independently extract data using pre-defined data extraction and assess the quality using the Risk of Bias tool for RCTs and Newcastle-Ottawa Scale for observational studies. We will use random-effects meta-analysis for each exposure-outcome association to calculate pooled estimates using the generic variance method. This systematic review will follow the Preferred Reporting Items for Systematic reviews and Meta-analyses guidelines. PROSPERO registration: CRD42023457368 (04/09/2023)

Continuous Transabdominal Fetal Pulse Oximetry (TFO) in Pregnant Ewe Models under Induced Fetal Hypoxia

Fetal heart rate monitoring is a poor predictor of fetal hypoxia for its high false-positive rate. Using a novel TFO, this study aims to demonstrate feasibility of continuous, non-invasive assessment of fetal arterial blood oxygen saturation (fSpO2) in hypoxic in-utero lamb models.

Review of optical methods for fetal monitoring in utero.

The current technology for monitoring fetal wellbeing during child birth is cardiotocography. However, CTG has high false positive rates that lead to unnecessary emergency Cesarean deliveries and false negatives that result in birth injuries. To curtail these issues, fetal pulse oximetery has been a topic of interest for many decades. Fetal pulse oximetry would yield the oxygen saturation of the fetus in utero and provide a more robust marker for clinicians to make decisions about performing emergency Cesarean deliveries. Here, we present a review of biomedical optical developments related to transabdominal fetal pulse oximetery in the biophotonics field and the challenges that must be overcome to make transabdominal pulse oximetry a clinical reality.

Estimation of Fetal Blood Oxygen Saturation from Transabdominally Acquired Photoplethysmogram Waveforms.

Transabdominal Fetal Pulse Oximetry (TFO) faces several challenges, including the acquisition of noisy Photoplethysmogram (PPG) signals that contain a mixture of maternal and weak fetal information and scarcity of the data points on which an estimation model can be calibrated. This paper presents a novel algorithm that addresses these problems and contributes to the estimation of fetal blood oxygen saturation from PPG signals sensed through the maternal abdomen in a non-invasive manner. Our approach is composed of two critical steps. First, we develop methods to approximate the contribution of pulsating and non-pulsating fetal tissue from the sensed mixed signal. Furthermore, we leverage prior information about the system under observation, such as the physiological plausibility of fetal SpO2 estimates, to mitigate measurement noise and infer additional data samples, enabling improvements in the inferred SpO2 estimation model. We have validated our approach in-vivo, using a pregnant sheep model with a hypoxic fetal lamb. Compared with gold standard SaO2 obtained from blood gas analysis, our fetal SpO2 estimation algorithm yields the cross-validation mean absolute error (MAE) of 6.29% and correlation factor of r=0.82.

Effectiveness of intrapartum fetal surveillance to improve maternal and neonatal outcomes: a systematic review and network meta-analysis

BACKGROUND:Cesarean delivery is the most common surgical procedure worldwide. Intrapartum fetal surveillance is routinely offered to improve neonatal outcomes, but the effects of different methods on the risk of emergency cesarean deliveries remains uncertain. We conducted a systematic review and network meta-analysis to evaluate the effectiveness of different types of fetal surveillance.METHODS:We searched MEDLINE, Embase and CENTRAL until June 1, 2020, for randomized trials evaluating any intrapartum fetal surveillance method. We performed a network meta-analysis within a frequentist framework. We assessed the quality and network inconsistency of trials. We reported primarily on intrapartum emergency cesarean deliveries and other secondary maternal and neonatal outcomes using risk ratios (RRs) and 95% confidence intervals (CIs).RESULTS:We included 33 trials (118 863 patients) evaluating intermittent auscultation with Pinard stethoscope/handheld Doppler (IA), cardiotocography (CTG), computerized cardiotocography (cCTG), CTG with fetal scalp lactate (CTG-lactate), CTG with fetal scalp pH analysis (CTG-FBS), CTG with fetal pulse oximetry (FPO-CTG), CTG with fetal heart electrocardiogram (CTG-STAN) and their combinations. Intermittent auscultation reduced the risk of emergency cesarean deliveries compared with other types of surveillance (IA v. CTG: RR 0.83, 95% CI 0.72–0.97; IA v. CTG-FBS: RR 0.71, 95% CI 0.63–0.80; IA v.CTG-lactate: RR 0.77, 95% CI 0.64–0.92; IA v. FPO-CTG: RR 0.75, 95% CI 0.65–0.87; IA v.FPO-CTG-FBS: RR 0.81, 95% CI 0.67–0.99; cCTG-FBS v. IA: RR 1.21, 95% CI 1.04–1.42), except STAN-CTG-FBS (RR 1.17, 95% CI 0.98–1.40). There was a similar reduction observed for emergency cesarean deliveries for fetal distress. None of the evaluated methods was associated with a reduced risk of neonatal acidemia, neonatal unit admissions, Apgar scores or perinatal death.INTERPRETATION:Compared with other types of fetal surveillance, intermittent auscultation seems to reduce emergency cesarean deliveries in labour without increasing adverse neonatal and maternal outcomes.

Reevaluation of intrapartum fetal monitoring using fetal oximetry: A review.

Although several studies reported the measurement of fetal oxygen saturation using fetal pulse oximetry (FPO) for evaluation of the fetal intrapartum condition, a systematic review of the seven randomized controlled trials (RCTs) provided no evidence to support FPO for intrapartum fetal monitoring. In the present review, we re-evaluate an overview for the use of FPO and seven RCTs of FPO. We reviewed numerous previous reports on FPO and seven RCTs of intrapartum FPO. RCTs were conducted with the main outcome measure being a reduction in the cesarean section rate. The largest trial with 5341 entries failed to show any reduction. The negative result from this RCT may be explained by the use of a different cutoff value for fetal oxygen saturation compared to the other RCT; in addition, there were differences in the indications for cesarean section due to dystocia and in the definition of non-reassuring fetal status (NRFS). An abnormal FPO value, defined as the fetal oxygen saturation value <30% for at least 10 min, is useful for making a diagnosis of fetal acidosis. A newly developed device, an examiner's finger-mounted tissue oximetry, accurately measures tissue oxygen saturation while overcoming the drawbacks of FPO, such as infection risk and slipping off of the sensor during descent of the fetal head. FPO (including the new device) with fetal heart rate monitoring in selected cases of NRFS may reduce the cesarean section rate.

Recovering the fetal signal in transabdominal fetal pulse oximetry

Non-invasive transabdominal fetal pulse oximetry (TFO) can provide physicians with a better metric of fetal well-being than currently-used fetal monitoring methods. There are two major challenges in this light-based measurement modality. One is in detecting the weak fetal signal at the surface of the maternal abdomen, and the other is in recovering the fetal signal from the diffuse reflectance measured, which contains a mixture of information about both maternal and fetal tissue. In this paper, we describe the TFO system we developed and evaluate its ability to recover the fetal signal in a preclinical setting. In particular, we assess its capability to measure the fetal signal over several thicknesses of maternal tissue and gauge the effectiveness of different approaches in removing the maternal influence from the mixed signal. Our results show that our TFO system, built using commodity low-cost components, can measure the highly-attenuated fetal signal through maternal tissue as thick as 5 cm. Furthermore, we determine that adaptive noise cancellation techniques are the most effective for separating the fetal signal from the maternally-influenced noise. These findings strongly support our TFO system's ability to perform well on a variety of different pregnant body types.

Signal Separation for Transabdominal Non-invasive Fetal Pulse Oximetry using Comb Filters.

Non-invasive fetal pulse oximetry is the application of reflection pulse oximetry to the abdomen of a pregnant woman. Light sources and detectors areplaced on the belly. Emitted photons travel through maternal and fetal tissue and back to the detectors. The captured photoplethysmogram (PPG) is a complex mixture of the maternal and fetal pulse curve. A purely fetal PPG in time domain is needed to estimate the oxygen level of the unborn child. In this work we describe the application of comb filters to separate the fetalfrom the maternal signal. Finite element simulations and phantom measurements are utilized to generate and measure synthetic signals at different heart rates and noise levels. Comb filters with peak frequencies matched to the fetal heart rate are applied to the mixed PPGs. The filtered signals prove that the extraction of the fetal signal is sufficient even at a distance between the maternal and the fetal signal magnitudes of around 80 dB. The resulting signal quality is sufficient for beat to beat analysis and feature extraction in the time domain. We conclude that comb filtering is a suitable signal separation method for non-invasive fetal pulse oximetry.

No. 197b-Fetal Health Surveillance: Intrapartum Consensus Guideline.

This guideline provides new recommendations pertaining to the application and documentation of fetal surveillance in the intrapartum period that will decrease the incidence of birth asphyxia while maintaining the lowest possible rate of obstetrical intervention. Pregnancies with and without risk factors for adverse perinatal outcomes are considered. This guideline presents an alternative classification system for antenatal fetal non-stress testing and intrapartum electronic fetal surveillance to what has been used previously. This guideline is intended for use by all health professionals who provide intrapartum care in Canada. Consideration has been given to all methods of fetal surveillance currently available in Canada. Short- and long-term outcomes that may indicate the presence of birth asphyxia were considered. The associated rates of operative and other labour interventions were also considered. A comprehensive review of randomized controlled trials published between January 1996 and March 2007 was undertaken, and MEDLINE and the Cochrane Database were used to search the literature for all new studies on fetal surveillance antepartum. The level of evidence has been determined using the criteria and classifications of the Canadian Task Force on Preventive Health Care (Table1). This consensus guideline was jointly developed by the Society of Obstetricians and Gynaecologists of Canada and the British Columbia Perinatal Health Program (formerly the British Columbia Reproductive Care Program or BCRCP) and was partly supported by an unrestricted educational grant from the British Columbia Perinatal Health Program. RECOMMENDATION 1: LABOUR SUPPORT DURING ACTIVE LABOUR: RECOMMENDATION 2: PROFESSIONAL ONE-TO ONE CARE AND INTRAPARTUM FETAL SURVEILLANCE: RECOMMENDATION 3: INTERMITTENT AUSCULTATION IN LABOUR: RECOMMENDATION 4: ADMISSION FETAL HEART TEST: RECOMMENDATION 5: INTRAPARTUM FETAL SURVEILLANCE FOR WOMEN WITH RISK FACTORS FOR ADVERSE PERINATAL OUTCOME: When a normal tracing is identified, it may be appropriate to interrupt the electronic fetal monitoring tracing for up to 30 minutes to facilitate periods of ambulation, bathing, or position change, providing that (1) the maternal-fetal condition is stable and (2) if oxytocin is being administered, the infusion rate is not increased (III-B). RECOMMENDATION 6: DIGITAL FETAL SCALP STIMULATION: RECOMMENDATION 7: FETAL SCALP BLOOD SAMPLING: RECOMMENDATION 8: UMBILICAL CORD BLOOD GASES: RECOMMENDATION 9: FETAL PULSE OXIMETRY: RECOMMENDATION 10: ST WAVEFORM ANALYSIS: RECOMMENDATION 11: INTRAPARTUM FETAL SCALP LACTATE TESTING.

Intrapartum Fetal Monitoring: Pathophysiology and Evolution of Various Techniques

Perinatal hypoxia has been a source of major concern for the pregnant woman and her obstetrician alike. The former was plagued by constant worries of neonatal morbidity and mortality and the latter, by constant threat of medical litigations. Intrapartum fetal monitoring (IPFM) played an important role in the attempt to establish equilibrium. Initially, intermittent auscultation was the only method of monitoring the well-being of fetus during labor. Further research led to the evolution of electronic fetal monitoring, scalp blood sampling, fetal pulse oximetry, ST-analysis of the fetal ECG and the use of sophisticated magnetism and infra-red optics. A trial using artificial intelligence in IPFM has recently reached its final phase. Even as more novel methods of monitoring continue to emerge, the perfect monitoring technique still remains to be discovered. Analysis made it evident that no single method was capable of distinguishing true cases of fetal distress from false one, sufficiently accurately. A combination of two or more methods is required for a reliable diagnosis to be obtained, and current treatment protocols should reflect this. The concurrent use of two or more monitoring methods in an algorithmic manner will go a long way in reducing the incidence of perinatal morbidity especially in high risk obstetric cases.

Development of a Two Channel Dynamic Phantom for Fetal Heart Rate and Pulse Oximetry Application

Development of a Two Channel Dynamic Phantom for Fetal Heart Rate and Pulse Oximetry Application

Photoplethysmographic waveform characteristics of newborns with coarctation of the aorta.

Fetal echocardiography, physical examination and pulse oximetry detect only half of coarctation of aorta (CoA) cases. We aimed to quantify delayed arrival and diminished amplitude of lower extremity photoplethysmographic (PPG) pulses relative to the right hand in affected patients. We studied 8 CoA infants and 32 healthy controls. The pulse arrival time difference between foot and hand (f-hTD) and pulse amplitude ratio (F/H) were measured on PPG signal waveforms by digitally-determining maxima and minima of systolic decrease of light transmission. Mann-Whitney test was used for group comparisons. In comparison to healthy newborns, CoA infants' PPG waveforms demonstrated prolonged f-hTD (mean±s.d. of 73.2±26.6 versus 35.2±8.3 ms, P<0.001) and lower F/H (0.57±0.26 versus 0.99±0.58, P=0.014). F-hTD and F/H are quantifiable from hand- and foot-derived PPG waveforms and are significantly different in CoA versus healthy newborns. Larger studies are needed to validate PPG for improved critical congenital heart disease screening.

Improved FPGA controlled artificial vascular system for plethysmographic measurements

Abstract The fetal oxygen saturation is an important parameter to determine the health status of a fetus, which is until now mostly acquired invasively. The transabdominal, fetal pulse oximetry is a promising approach to measure this non-invasively and continuously. The fetal pulse curve has to be extracted from the mixed signal of mother and fetus to determine its oxygen saturation. For this purpose efficient algorithms are necessary, which have to be evaluated under constant and reproducable test conditions. This paper presents the improved version of a phantom which can generate artificial pulse waves in a synthetic tissue phantom. The tissue phantom consists of several layers that mimic the different optical properties of the fetal and maternal tissue layers. Additionally an artificial vascular system and a dome, which mimics the bending of the belly of a pregnant woman, are incorporated. To obtain data on the pulse waves, several measurement methods are included, to help understand the behavior of the signals gained from the pulse waves. Besides pressure sensors and a transmissive method we integrated a capacitive approach, that makes use of the so called “Pin Oscillator” method. Apart from the enhancements in the tissue phantom and the measurements, we also improved the used blood substitute, which reproduces the different absorption characteristics of fetal and maternal blood. The results show that the phantom can generate pulse waves similar to the natural ones. Furthermore, the phantom represents a reference that can be used to evaluate the algorithms for transabdominal, fetal pulse oximetry.

Principle study on the signal connection at transabdominal fetal pulse oximetry

Abstract Transabdominal fetal pulse oximetry is an approach to measure oxygen saturation of the unborn child non-invasively. The principle of pulse oximetry is applied to the abdomen of a pregnant woman, such that the measured signal includes both, the maternal and the fetal pulse curve. One of the major challenges is to extract the shape of the fetal pulse curve from the mixed signal for computation of the oxygen saturation. In this paper we analyze the principle kind of connection of the fetal and maternal pulse curves in the measured signal. A time varying finite element model is used to rebuild the basic measurement environment, including a bulk tissue and two independently pulsing arteries to model the fetal and maternal blood circuit. The distribution of the light fluence rate in the model is computed by applying diffusion equation. From the detectors we extracted the time dependent fluence rate and analyzed the signal regarding its components. The frequency spectra of the signals show peaks at the fetal and maternal basic frequencies. Additional signal components are visible in the spectra, indicating multiplicative coupling of the fetal and maternal pulse curves. We conclude that the underlying signal model of algorithms for robust extraction of the shape of the fetal pulse curve, have to consider additive and multiplicative signal coupling.

Association of Cervical Effacement With the Rate of Cervical Change in Labor Among Nulliparous Women.

To assess the association of cervical effacement with the rate of intrapartum cervical change among nulliparous women. We conducted a secondary analysis of a prospective trial of intrapartum fetal pulse oximetry. For women who had vaginal deliveries, interval-censored regression was used to estimate the time to dilate at 1-cm intervals. For each given centimeter of progressive cervical dilation, women were divided into those who had achieved 100% cervical effacement and those who had not. The analysis was performed separately for women in spontaneous labor and those who were given oxytocin. A total of 3,902 women were included in this analysis, 1,466 (38%) who underwent labor induction, 1,948 (50%) who underwent labor augmentation (combined for the analysis), and 488 (13%) who labored spontaneously. For women in spontaneous labor, the time to dilate 1 cm was shorter for those who were 100% effaced starting at 4 cm of cervical dilation (P=.01 to <.001). For women who received oxytocin, the time to dilate 1 cm was shorter for those who were 100% effaced throughout labor (P<.001). The rate of cervical dilation among nulliparous women is associated with not only the degree of cervical dilation, but also with cervical effacement. ClinicalTrials.gov, www.clinicaltrials.gov, NCT00098709.

Evaluation of Clinical Diagnosis of Fetal Distress and Perinatal Outcome in a Low Resource Nigerian Setting.

Fetal distress has been shown to contribute to the increasing caesarean section rate. There has been controversy on the usefulness of clinical diagnosis of fetal distress using only the intermittent counting of the fetal heart rate and/or passage of meconium-stained liquor. To evaluate the clinical diagnosis of fetal distress and the perinatal outcome. This was a retrospective study in which the case records of the patients, who were diagnosed of fetal distress at Federal Teaching Hospital, Abakaliki, Nigeria, from January 1, 2008 to December 31, 2014, were collated. The statistical analysis was done using the Statistical Package for Social Sciences version 17 software (SPSS Inc., Chicago IL, USA). Out of the 15,640 deliveries carried out within the study period, 3,761 (24.05%) deliveries were through caesarean section. A total of 326 (8.9%) of the 3,761 caesarean sections were due to fetal distress within the study period. More so, a total of 227 (70.9%) babies were born with ≥ 7 Apgar score at the 1(st) minute of delivery. The perinatal mortality rate was 31.25 per 1000 deliveries. Though birth asphyxia was recorded more on babies of mothers that had fresh meconium-stained liquor and whose decision-intervention interval was more than 30 minutes when compared with those without any of the two conditions, there was no statistical significant difference between them. The clinical diagnosis of fetal distress is accurate in 29.1% of the cases. However, it has led to an unnecessary caesarean section in the remaining 70.9% of the parturients. In order to reduce this high trend of unnecessary caesarean sections due to clinical diagnosis of fetal distress in this environment, antepartum fetal assessment with non-stress test or biophysical profile and intrapartum use of continuous electronic fetal monitoring should be used to confirm or refute the fetal distress before any surgical intervention. Fetal blood sampling and fetal pulse oximetry should be performed in event of non- re-assuring or abnormal cardiotocography.

Simulation based investigation of source-detector configurations for non-invasive fetal pulse oximetry

Abstract Transabdominal fetal pulse oximetry is a method to monitor the oxygen supply of the unborn child non-invasively. Due to the measurement setup, the received signal of the detector is composed of photons coding purely maternal and photons coding mixed fetal-maternal information. To analyze the wellbeing of the fetus, the fetal signal is extracted from the mixed component. In this paper we assess source-detector configurations, such that the mixed fetal-maternal components of the acquired signals are maximized. Monte-Carlo method is used to simulate light propagation and photon distribution in tissue. We use a plane layer and a spherical layer geometry to model the abdomen of a pregnant woman. From the simulations we extracted the fluence at the detector side for several source-detector distances and analyzed the ratio of the mixed fluence component to total fluence. Our simulations showed that the power of the mixed component depends on the source-detector distance as expected. Further we were able to visualize hot spot areas in the spherical layer model where the mixed fluence ratio reaches the highest level. The results are of high importance for sensor design considering signal composition and quality for non-invasive fetal pulse oximetry.