RESUMO
Characteristics of uterine muscle action potentials in 100 gravidas with symptoms of preterm labor or imminent abortion (presence of contractions with cervical changes) from 18th till the 32nd weeks of pregnancy are analysed. Twenty four gravidas with uncomplicated pregnancy were monitored electromyographically from the 20th weeks until term, once a week. There was low electrical activity in uncomplicated pregnancies up to 7 days before labor. A similar trend was observed in pregnancies that were finished before term. But, in symptomatic pregnancies finished preterm, the index of uterine muscle electrical activity (expressed in the percentage of voltage plus frequency) was continuously, although not significantly, above the values in symptomatic and asymptomatic term pregnancies. In only 2 out of 18 (11.1%) before term terminated pregnancies and in 45 out of 82 (54.9%) in term accomplished pregnancies, was electrical silence was registered during clinical symptoms (p less than 0.01). In preterm accomplished pregnancies, higher voltages and more frequent occurrence of biphasic and polyphasic spikes were registered (p less than 0.05), although the single parameter was of no prognostic significance. With a successful tocolytic treatment, the index of uterine muscle electrical activity was significantly reduced (from 57.16 to 20.86, t = 2.52, p less than 0.02) and was similar to that registered in symptomatic term pregnancies subjected to no tocolytic treatment. Although intravenous tocolysis was shown diminish voltage and frequency, in preterm delivered pregnancies no reduction in electrical activity was observed. Uterine electromyography could be used as a predictor of successful or unsuccessful tocolytic treatment.
