Active phase labor arrest: Revisiting the 2-hour minimum

OBJECTIVE: To generate contemporary uterine activity and labor progress dat a for oxytocin-augmented labor, and assess whether 2 hours of active phase labor arrest with at least 200 Montevideo units justifies cesarean delivery . METHODS: Five hundred and one consecutive spontaneously laboring term women with abnormally progressive labor were managed by a standardized protocol: oxytocin and intrauterine pressure catheter with an intent to sustain at l east 200 Montevideo units for 4 hours or more before cesarean for labor arr est. Uterine activity was measured, and maternal and neonatal outcomes were evaluated. With a sample of this size, the upper 95% confidence interval l imit for an event with an observed rate of 1% is below 3%. RESULTS: During oxytocin augmentation, nulliparas who were delivered vagina lly dilated at a median rate of 1.4 cm/hour versus 1.8 cm/hour for parous w omen. In both groups, the 5th percentile of cervical dilation rate was 0.5 cm/hour. Thirty-eight women experienced labor arrest for over 2 hours despi te at least 200 sustained Montevideo units; 23 (61%) achieved a vaginal del ivery. Plates of chorioamnionitis and endometritis for the 38 women were 26 %. None of their infants sustained a serious complication, including brachi al plexus injury, even though dime of die 23 vaginal deliveries (13%) were complicated by shoulder dystocia. CONCLUSION: These data demonstrate that oxytocin-augmented labor proceeds a t substantially slower rates than spontaneous labor, and support our previo us contention that the criteria of labor arrest for 2 hours, despite at lea st 200 sustained Montevideo units, are insufficiently rigorous for the perf ormance of cesarean. (C) 2001 by the American College of Obstetricians and Gynecologists.