Uterine activity during pregnancy and labor assessed by simultaneous recordings from the myometrium and abdominal surface in the rat

OBJECTIVES: The aim of this study was to analyze records of uterine electrical activity made from the abdominal surface of pregnant and laboring rats to examine whether similar quantitative information can be extracted as from direct recording from the uterine muscle. STUDY DESIGN: Electrical activity during pregnancy (nonlabor, days 18 to 22), term labor (day 22), and preterm labor (onapristone injected on day 18, delivery on day 19) was measured with use of electrodes attached to the uterine wall and to the abdominal surface. The fast Fourier transform and wavelet transforms were obtained for representative electromyographic bursts. Power spectra were generated. Intrauterine pressure was also measured. RESULTS: (1) Several parameters have been identified for use in following up the progressive increase in uterine activity that occurs in preparation for and during labor. Analyses of amplitude, frequency, and percent time active represent a convenient method for objectively determining the efficiency of uterine contraction. (2) Most of the changes in these parameters appear in the last 24 hours before delivery. (3) Although the uterine electromyographic signals on the abdominal surface are attenuated, the abdominal surface signals are generally similar to the signals obtained from the uterine muscle during pregnancy and during preterm and term labor. (4) The characteristics of onapristone-induced preterm labor are generally similar to those of spontaneous term labor. CONCLUSIONS: Recording of uterine electromyographic activity from the abdominal surface may be useful in following the progression of pregnancy and in predicting and diagnosing labor.