ELECTRICAL-ACTIVITY OF THE HUMAN UTERUS DURING PREGNANCY AS RECORDED FROM THE ABDOMINAL SURFACE

Objective: To validate the possibility that human uterine electrical e vents (electromyographic signals) can be recorded and characterized fr om the abdominal surface during pregnancy. Methods: The gestational ag es ranged from 20 to 43 weeks. The study included patients at term but not in labor, patients in active labor (term and preterm), postpartum patients, and patients followed monthly during their pregnancy (n = 4 0). Uterine electrical activity in the frequency range of 0.3-50 Hz wa s recorded using bipolar electrodes placed on the abdominal surface. I n some patients, intrauterine pressure also was measured. Power spectr al analysis was performed using the fast Fourier transform. Results: T hroughout most of pregnancy, uterine electrical activity was minimal, consisting of infrequent and low-amplitude electromyographic bursts. W hen bursts occurred before labor, they often corresponded to perceptio ns of contractility by the patient. During term and preterm labor, bur sts of electromyographic activity were frequent and of large amplitude and were correlated with large transient changes in the intrauterine pressure and with pain. Fast Fourier transform analysis of the bursts during active term labor demonstrated a peak frequency of 0.71 +/- 0.0 5 Hz, compared with 0.48 +/- 0.03 Hz before labor. Spectral analysis a lso showed a fivefold increase in the peak energy levels of the bursts during term labor (60.2 +/- 13.87 mu Vs) and preterm labor (62.3 +/- 22.93 mu Vs) compared with earlier in gestation (11.36 +/- 4.03 mu Vs at 27-36 weeks; P < .05). Conclusion: Recording of uterine electromyog raphic activity from the abdominal surface is a reliable method to fol low the evolution of uterine contractility during pregnancy and during term and preterm labor. Further studies will define the usefulness of this noninvasive technology in the prediction and management of labor . (C) 1997 The American College of Obstetricians and Gynecologists.