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

Significance: 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.

Aim: To address this concern, we present a noninvasive method for precise fetal oxygenation level monitoring using time-domain near-infrared spectroscopy (TD-NIRS).

Approach: 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.

Results: 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.

Conclusions: The results suggest a significant potential for the use of TD-NIRS to noninvasively and safely monitor the fetal oxygenation level.