Maximum Dose Rate of Intrapartum Oxytocin Infusion and Associated Obstetric and Perinatal Outcomes

Abstract

OBJECTIVE: Despite lack of evidence for a safety threshold for oxytocin dose rate, many hospital protocols specify a maximum rate. We investigated whether exceeding 20 milliunits/min of oxytocin was associated with adverse outcomes. METHODS: This is a secondary analysis of a double-blind, single-center, randomized controlled trial of nulliparous patients with singleton gestations at 36 weeks of gestation or later who presented in spontaneous labor randomized 1:1 to either a high-dose oxytocin titration regimen (initial-incremental rate of 6 milliunits/min) or standard-dose titration regimen (initial-incremental rate of 2 milliunits/min) for labor augmentation. A maximum oxytocin dose rate limit was not specified in the study protocol. For this secondary analysis, outcomes of participants who received oxytocin and exceeded a dose rate of 20 milliunits/min at any point in labor were compared with those whose rate remained at 20 milliunits/min or less. In addition, the cumulative proportions of labor and birth outcomes were calculated for each maximum dose rate of oxytocin reached among this study cohort. RESULTS: Of the 1,003 participants in the parent trial, 955 (95.2%) received oxytocin, as planned, and were included, with 190 (19.9%) exceeding a maximum dose rate of 20 milliunits/min. Those who exceeded 20 milliunits/min were older and were more likely to have rupture of membranes as their trial entry indication, have hypertensive disorders of pregnancy, receive intrapartum magnesium sulfate infusion, and receive oxytocin for longer. Those whose maximum rates exceeded 20 milliunits/min underwent cesarean delivery more frequently, but the majority (74%) still delivered vaginally. In multivariable analyses, there were no significant associations between maximum oxytocin dose rates greater than 20 milliunits/min and cesarean delivery (adjusted odds ratio [aOR] 1.57, 95% CI 1.00–2.46), peripartum infection (aOR 0.69, 95% CI 0.41–1.19), postpartum hemorrhage (aOR 1.37, 95% CI 0.70–2.71), or neonatal intensive care unit (NICU) admission (aOR 1.72, 95% CI 0.89–3.31). Although 85% of spontaneous vaginal deliveries occurred at maximum oxytocin dose rates of 20 milliunits/min or less, vaginal deliveries continued to occur at higher maximum dose rates. The cumulative proportions of NICU admissions and composite severe neonatal morbidity and mortality cases increased with increasing oxytocin dose rates even with maximum oxytocin dose rates at 20 milliunits/min or less. CONCLUSION: In multivariable analyses, there are no significant differences in maternal or perinatal adverse outcomes based on exceeding 20 milliunits/min of oxytocin. These data suggest that oxytocin dosing should be individualized to each patient and not be based on arbitrary thresholds. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, NCT02487797.