Comparison of spontaneous, oxytocin-stimulated, and hypertonic saline-induced labor by different methods of record analysis

Intrauterine pressure recordings were made during the active phase of labor in 64 patients. On-line electronic integration of the area under the pressure curve was used as a measure of uterine activity. A total of 204 hours of labor including 4,224 individual contractions were analyzed by (1) average pressure (integrator method), (2) Montevideo units, (3) Alexandria units, and (4) frequency distribution. Comparisons were made between spontaneous labor, oxytocin-stimulated labor, and hypertonic saline-induced labor. Oxytocin-stimulated labor and hypertonic saline-induced labor show increases in amplitude and frequency of contractions when compared with spontaneous labor. Concomitant increases in total uterine activity were noted by all methods of measurement. In this series, both hypertonic saline-induced and oxytocin-stimulated labor are different from spontaneous labor whether measured in Montevideo units, Alexandria units, or average pressure. Electronic integration of the pressure signal is recommended as a method of measuring uterine activity in physical units (mm. Hg).