The disclosed system determines a fetal blood oxygenation level. During operation, the system activates two or more light sources, having different wavelengths, which are positioned on the abdomen of a pregnant mammal to direct light into the maternal abdomen toward a fetus. Next, the system receives a set of mixed signals from a set of photodetectors, which are positioned at different locations on the maternal abdomen to receive reflected light that traverses both maternal and fetal tissue. The system then performs a filtering operation that removes signal components associated with a maternal heart rate and a maternal respiration rate from the set of mixed signals to produce a set of fetal signals. Next, the system combines the set of fetal signals to produce a composite fetal signal. Finally, the system determines the fetal blood oxygenation level by performing a pulse-oximetry computation based on the composite fetal signal.
