Abstract
Fetal heart rate is known as one of the best representations of the fetal situations in labor. The heart rate is counted by means of FECG or FPCG obtained from the maternal abdominal wall or direct ECG from the fetal scalp after rupture of the amnionic sac. However, these methods are not satisfactory by the reasons of poor signal to noise ratio, difficulty in continuous monitoring, and so on. Accordingly, we applied the radiotelemetry to measurement of FHR, in which an adequate size transmitter combined with electrodes was inserted into the uterine space. The direct FECG was transmitted throughout all stages of labor and received by a commercial short wave radio receiver placed near by. And ECG of the newborn baby was also taken from the axilla with ease by a clip electrode-transmitter consisting a clip electrode for adult limb lead and a small transmitter. The carrier frequency was chosen at about 6 Mc/s and the amplitude was modulated by the signal. The size and the form of the transmitter were determined to allow easy insertion to uterine space, complete contact with the amnionic sac and easy exchange of the battery, and not to behave as a foreign body and not to being exhausted by delivery. After construction on the board of printed wiring, the transmitter was molded by silicon rubber. to prevent from injuring the body and to be insulated from the tissues. The total weight and volume were 15 g and 9 cm3, respectively. Drain current was 200, uA with the receiving range of about 1.5 meter. ECGs of six fetuses including three cases of cesarean section were investigated throughout labor and delivery. Especially interesting results were obtained of FHRs before and after rupture of the amnionic sac, labor, delivery and ligation of the umbilical cord and during cesarean section.
