Uterine activity patterns in uterine rupture: a case-control study.

Objective: To determine whether uterine activity patterns are associated with intrapartum uterine rupture.
Methods: Because of the infrequency of uterine rupture, a case-control design was implemented. Cases were women who sustained uterine ruptures during a trial of labor, resulting in a neurologically impaired neonate. Controls were women who had a successful vaginal birth after cesarean (VBAC) or vaginal delivery with no history of uterine scar. The uterine activity patterns of cases were compared with those of each control group for number of contractions per hour, uterine tetany (contraction longer than 90 seconds), and uterine hyperstimulation (five or more contractions in a 10-minute period).
Results: The final study population consisted of 18 rupture patients, 35 VBAC patients, and 33 spontaneous vaginal delivery patients. Women in the rupture group had fewer contractions per hour (15.8+/-7.3) than VBAC (19.7+/-5.5) (P < .05) or spontaneous delivery group (19.4+/-6.6) (P < .10). VBAC patients were five times as likely to have 16 or more contractions per hour than were rupture patients, 95% confidence interval [CI] 1.3, 21.3, P < .02). Patients who had spontaneous delivery were 3.5 times more likely to have 16 or more contractions per hour than were rupture patients (95% CI 0.9, 14.1, P = .08). The rupture group had equal or less uterine tetany than did the controls.
Conclusion: Uterine activity patterns and oxytocin use do not appear to be associated with the occurrence of intrapartum uterine rupture.