Frequent measurement of pH and PCO2 levels of fetal blood during labour provides an insight into the presence and nature of fetal asphyxia, effectiveness of in utero resuscitation and the need for operative delivery. A pH measuring system utilizing a hydrogen ion-selective polymer membrane built into a fetal probe suitable for making intermittent measurements on the fetal scalp during labour is described. Probe design, construction of electrodes and preliminary results obtained using the system in vitro are presented.
