a subcutaneous radiation reflection probe for measuring oxygen saturation in living tissue includes an elongate drive shaft on one end of which is detachably coupled a mounting cup . the mounting cup includes a hollow for receiving and holding a base element on which is mounted a spiral needle which coils outwardly from the mounting cup to terminate in a pointed end . a window is formed in the spiral needle near the pointed end thereof for receiving and holding a radiation emitter , such as a light emitting diode . a radiation detector is disposed on the base element within the coil of the spiral needle . the probe may be used to measure oxygen saturation in living tissue , such as a fetal scalp , by inserting the mounting cup and drive shaft through an introducer into a woman &# 39 ; s vagina until the spiral needle contacts the fetal scalp . the drive shaft may then be rotated so that the spiral needle rotates into the scalp , after which energizing pulses are applied to the radiation emitter to cause it to emit radiation and illuminate the fetal scalp tissue into which the needle is inserted . the radiation detector detects a portion of this radiation , depending upon the oxygen saturation of the tissue , and develops a signal to thus provide a measure of the oxygen saturation .