Continuous telemetric monitoring of fetal oxygen partial pressure during labor

Upright or ambulatory birth positions are favorable for fetal oxygenation. Studies of fetal oxygenation with regard to maternal position require free maternal mobility. Therefore, telemetry for a fetal sensor for such investigations is a pre-requisite. Telemetry-if technically feasible-could enable monitoring of fetal oxygen partial pressure using an existing sensor without restricting the mobility of the parturient woman. We have developed a telemetry system for use with a fetal transcutaneous partial oxygen pressure sensor (ttcpO(2)) and have studied effects of maternal position and position changes during normal labor.

The monitoring system consists of three parts: the telemetry unit with the ttcpO(2) sensor to transmit the tcpO(2) and the heating output telemetrically, a modified CTG monitor and a personal computer storing the measurements. All data were plotted on the CTG recording paper and fed into a new purpose-designed software, displaying fetal heart rate, the uterine contraction intensity, ttcpO(2) and the heating output. Three laboring women, randomly and successively adopting "classical birth positions" (supine or side positions), sitting or vertical or walking position, were studied.

Fetal heart rate, uterine contractions, ttcpO(2) and heating output are influenced by the birth positions and by changes of the birth position. In the classical supine and side position there seemed to be lower fetal oxygenation. Sitting, standing and especially walking were more favorable.

Telemetry is useful to study a possible clinical benefit of individual birth positions.