Association between duration of intrapartum oxytocin exposure and obstetric hemorrhage.

PURPOSE: Prolonged duration of intrapartum oxytocin exposure is included as a risk factor within widely adopted obstetric hemorrhage risk stratification tools. However, the duration of exposure that confers increased risk is poorly understood. This study aimed to assess the association between duration of intrapartum oxytocin exposure and obstetric blood loss, as measured by quantitative blood loss, and hemorrhage-related maternal morbidity. METHODS: This was a retrospective cohort study of all deliveries from 2018 to 2019 at a single medical center. We included patients who had received any intrapartum oxytocin, and we categorized them into 1 of 5 groups: > 0-2, ≥ 2-4, ≥ 4-6, ≥ 6-12, and ≥ 12 h of intrapartum oxytocin exposure. The primary outcomes were mean quantitative blood loss, proportion with obstetric hemorrhage (defined as quantitative blood loss ≥ 1000 mL), and proportion with obstetric hemorrhage-related morbidity, a composite of hemorrhage-related morbidity outcomes. Secondary outcomes were hemorrhage-related pharmacologic and procedural interventions. A stratified analysis was also conducted to examine primary and secondary outcomes by delivery mode. RESULTS: Of 5332 deliveries between January 1, 2018 and December 31, 2019 at our institution, 2232 (41.9%) utilized oxytocin for induction or augmentation. 326 (14.6%) had exposure of > 0-2 h, 295 (13.2%) ≥ 2-4 h, 298 (13.4%) ≥ 4-6 h, 562 (25.2%) ≥ 6-12 h, and 751 (33.6%) ≥ 12 h. Across all deliveries, there was higher mean quantitative blood loss (p < 0.01) as well as increased odds of obstetric hemorrhage (adjusted odds ratio [aOR] 1.52, 95% confidence interval [CI] 1.21-1.91) for those with ≥ 12 h of oxytocin compared to all groups between > 0-12 h of exposure. In our stratified analysis, ≥ 12 h of oxytocin exposure was associated with higher mean quantitative blood loss (p = 0.04) and odds of obstetric hemorrhage in vaginal deliveries (aOR 1.47, 95% CI: 1.03-2.11), though not in cesarean deliveries (aOR 1.16, 95% CI 0.82-1.62). There were no differences in proportion with obstetric hemorrhage-related morbidity across all deliveries (p = 0.40) or in the stratified analysis. CONCLUSION: Intrapartum oxytocin exposure of ≥ 12 h was associated with increased quantitative blood loss and odds of obstetric hemorrhage in vaginal, but not cesarean, deliveries.