Non-invasive detection of instantaneous fetal hypoxemia in large animal model of pregnancy

Cardiotocography (CTG) has a high false positive rate for the detection of babies at risk of birth asphyxia. Transabdominal Fetal Pulse Oximetry (TFO) has the potential to supplement CTG by enabling non-invasive measurement of fetal arterial blood oxygen saturation (fSpO₂). Previous attempts at TFO were limited to intermittent measurements using highly specialized and precise instruments. We present a TFO system, utilizing multiple commodity silicon photo-detectors to acquire mixed maternal-fetal PPG signals, for non-invasive and continuous detection of fetal instantaneous normoxia vs. hypoxemia status, relative to a user-specified threshold. Data from controlled de-saturation experiments using pregnant ewes with an in-utero hypoxic lamb model, from a total of <i>n</i> = 8 hypoxic rounds (length = 34.5 ± 12 min), is used to validate the technology. The multi-layer perceptron model is used for information fusion, and fetal arterial blood oxygen saturation obtained from blood gas analysis is used as a gold standard. The method detects instantaneous hypoxemia (fSpO₂ <30%) with 87.6% accuracy. Cross-validation shows an average sensitivity of 88.2% and specificity of 71.2%. The receiver operating characteristic (ROC) curves showed strong discrimination abilities in all cross-validation iterations (AUC = 0.87). This study underscores TFO's promise for accurate detection of instantaneous fetal hypoxemia relative to a user-defined threshold value, and for contribution to enhancement of intrapartum fetal monitoring in the longer term.