Use of A Novel Transabdominal Fetal Pulse Oximeter (TFO) In Human Pregnancy: A Proof-of-Concept

The performance of novel TFO was reported in the pregnant ewe model in our laboratory. To advance TFO on the translational spectrum, this study aims to demonstrate and evaluate if TFO can acquire human fetal heart rate (FHR) signals in non-stress testing (NST) as a proof-of-concept. Sensing FHR is a precursor to measurement of fetal oxygen saturation in humans. Consented eight ongoing pregnancies undergoing NST that met inclusion criteria for the study: 18-40 years old, singleton, and ≥36 weeks’ gestation at the time of data acquisition. Study is approved by UC Davis Health IRB and NSF-funded. Additional data include patient demographics, vital signs, patients’ skin color compared to standard validated skin color scale (Skin Tone Guide, Pantone, Carlstadt NJ), and sonographically-derived distances from maternal skin to closest fetal part. At each NST session, 15 to 20 minutes TFO dataset was collected. Reference FHR and maternal heart rate (MHR) were obtained using finger pulse oximetry and cardiotocography for a post hoc comparison and correlation with the TFO readings. Adaptive noise cancellation and frequency-domain analysis were used to extract heart rates from TFO readings and statistically analyzed. Table 1 summarizes the characteristics of the 8 subjects in the study. The overall root-mean-square error (RMSE) was 9.72 beats-per-minute (BPM) for FHR, and 4.43 BPM for MHR. The overall mean-absolute error (MAE) was 7.64 BPM for FHR and 1.79 BPM for MHR. The Bland-Altman showed a mean bias ± standard deviation (SD) between TFO and referenced FHR measurements as -3.90±8.92 BPM and the limits of agreement were -21.37 to 13.58 BPM (Fig. 1). This proof-of-concept study determined that TFO device can discriminate fetal heart signal from maternal heart signal in humans via optical photoplethysmography measurements. This is a prerequisite step to enable fetal oxygen saturation measurement in humans using TFO. Future research will focus on improving the device prototype to reduce the error in detecting FHR, as well as conducting intrapartum studies.View Large Image Figure ViewerDownload Hi-res image Download (PPT)