Abstract: To determine the oxygen saturation and other parameters of blood flowing in a fetus positioned in the uterus by detecting the pulsation of the blood in the birthing process from the rupture of the water membrane to the delivery of the baby. An opening is formed near the distal end of a curved support member and both light-emitting portion and light-receiving portion are positioned in the opening as they are spaced apart by a specified gap in which the head of a fetus is rested for detecting the pulsation of blood using measurements of transmitted light.