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 el ectrical activity made from the abdominal surface of pregnant and labo ring rats to examine whether similar quantitative information can be e xtracted as from direct recording from the uterine muscle. STUDY DESIG N: Electrical activity during pregnancy (nonlabor, days 18 to 22), ter m labor (day 22), and preterm labor (onapristone injected on day 18, d elivery 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 electromyogra phic bursts. Power spectra were generated. Intrauterine pressure was a lso 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, fr equency, and percent time active represent a convenient method for obj ectively determining the efficiency of uterine contraction. (2) Most o f the changes in these parameters appear in the last 24 hours before d elivery. (3) Although the uterine electromyographic signals on the abd ominal surface are attenuated, the abdominal surface signals are gener ally similar to the signals obtained from the uterine muscle during pr egnancy and during preterm and term labor, (4) The characteristics of onapristone-induced preterm labor are generally similar to those of sp ontaneous term labor CONCLUSIONS: Recording of uterine electromyograph ic activity from the abdominal surface may be useful in following the progression of pregnancy and in predicting and diagnosing labor.