Uterine activity among a diverse group of patients at high risk for preterm delivery.

In this study, 98 patients with early premature rupture of membranes (PROM), postoperative recuperation, placenta previa, or blunt abdominal trauma were assessed for uterine contractions with an ambulatory uterine activity monitor. Uterine irritability manifested by low-amplitude, high-frequency contractions of 30 seconds' duration or less was prevalent in all groups but decreased as the patients were stabilized and diminished or disappeared in those who did not develop preterm labor. In the 18 women who developed preterm labor, daily uterine activity monitoring detected contractions 24-48 hours before clinical symptoms of preterm labor and/or vaginal bleeding occurred. A number of patients with early PROM and placenta previa had low-amplitude, high-frequency contractions, and the majority occurred in those who subsequently developed preterm labor.