Studies on the measurement of uterine contraction by the impedance-variance of maternal abdominal wall (author's transl)

An electronic system for the detection of uterine contractions by impedance measurement of the maternal abdominal wall, where the placenta attached to the anterior uterine wall confirmed by using B-mode ultrasonic method, was evaluated in 74 subjects. Simultaneous recordings of uterine contractive activity with conventional external recording system were made. Impedance recordings were evaluated and compared with the external recordings. The available evidence from this study indicated that 88.31% of uterine contractions were accurately detected and the onset, peak and end of each uterine contractions was reliable parameters of impedance measurement. The uterine contractions which seemed to be weaker in second trimester and difficult to record by the usage of external method were clearly detectable by the method. However on the place of the maternal abdomen where the placenta was not attached, impedance recordings did not show corresponding response with each uterine contractions. It was indicated that impedance recordings on the localization of the placenta mainly represented the change of intraplacental blood volume following by uterine contractions. The advantages of this method consisted in the patients comfort and easy application of the recording electrodes, but the usefulness of the method was limited to the cases of anterior localization of the placenta, namely 50% of the whole pregnant women.