Oxytocin dose and the risk of uterine rupture in trial of labor after cesarean

Objective: To examine the association between uterine rupture and oxytocin use in trial of labor after cesarean. Methods: A case-control study was performed. Cases were all women with uter ine ruptures who received oxytocin during a trial of labor after a single c esarean delivery within a 12-year period (n = 24). Four controls undergoing trial of labor after a single cesarean delivery were matched to each case by 500 g birth weight category, year of birth, and by induction or augmenta tion (n = 96). The study had an 80% power to detect a 40% increase in oxyto cin duration or a 65% increase in total oxytocin dose. Results: No significant differences were seen in initial oxytocin dose, max imum dose, or time to maximum dose. Although women with uterine ruptures ha d higher exposure to oxytocin as measured by mean total oxytocin dose (544 mU higher) and oxytocin duration (54 minutes longer), these differences wer e not statistically significant. Women with uterine rupture who received ox ytocin were more likely to have experienced an episode of uterine hyperstim ulation (37.5% compared with 20.8%, P = .05). However, the positive predict ive value of hyperstimulation for uterine rupture was only 2.8%. Conclusion: Although no significant differences in exposure to oxytocin wer e detected between cases of uterine rupture and controls, the rarity of ute rine rupture limited our power to detect small differences in exposure. In women receiving oxytocin, uterine rupture is associated with an increase in uterine hyperstimulation, but the clinical value of hyperstimulation for p redicting uterine rupture is limited. (C) 2001 by The American College of O bstetricians and Gynecologists.