Why is there an occasional transient rise in saturation values during contractions?
Some investigators have suggested that this event reflects a true transient rise in fetal saturation. It is more likely an artifact of pulse oximetry caused by blood being squeezed out of the tissue in the region under the sensor. Some light shunts through exsanguinated skin and tissue and reaches the photodetector, causing a measurement error. Earlier Nellcor sensor prototypes showed a higher incidence of this condition than the current model FS-14 Fetal Sensor, which has been redesigned to reduce these reading artifacts.
