Noninvasive monitoring of fetal tissue oxygenation level using time-domain NIRS

Fetal oxygenation level is a critical indicator of fetal health throughout pregnancy and labor. Existing clinical devices predominantly employ invasive techniques, posing risks to both the fetus and the mother. To address this concern, we present a noninvasive method for precise fetal oxygenation level monitoring using time-domain near-infrared spectroscopy (TD-NIRS). Our method leverages the advantages of time-domain information for accurate separation of optical properties from two distinct layers, thereby enabling noninvasive detection of deep tissue oxygenation levels. We validate the proposed method via Monte Carlo simulations and develop a fiber-based TD-NIRS prototype system. In a two-layer tissue phantom experiment, the system accurately estimates the deep-layer absorption coefficient. We further demonstrate the ability of our prototype system to detect changes in the tissue oxygenation index (TOI) through in vivo experiments: (1) TOI measurements of the human forearm with a tissue phantom and (2) transabdominal fetal monitoring on a pregnant ewe. The results suggest a significant potential for the use of TD-NIRS to noninvasively and safely monitor the fetal oxygenation level.