Modern analysis of pathologic uterine rings.

A computerized medical record search of 61,406 live births from January 1, 1990, through December 31, 1994, identified 14 cases of pathologic uterine rings. This yielded an incidence of pathologic uterine rings of 0.02% of all live births. In a retrospective, matched study design, three control subjects having vaginal delivery and three having cesarean delivery were matched with each case of pathologic uterine ring for age, race, parity, estimated gestational age, single or multiple gestation, primary or repeat cesarean section, and indication for the cesarean delivery. Comparison with controls who had cesarean section showed no significant differences in duration of labor, rupture of membranes, use of oxytocin, or fetal head position. Pathologic uterine rings continue to occur in modern obstetrics, but their reported incidence has decreased. These data suggest that the characteristics of parturition have no clear association with the formation of a pathologic uterine ring.