Is epidural analgesia an independent risk factor for OASIS? A population-based cohort study

Introduction: To evaluate whether epidural analgesia is an independent risk factor for OASIS. Methods: A population-based cohort study including all women who delivered by spontaneous vaginal delivery or by instrumental delivery beyond 24 weeks gestation was conducted. Deliveries occurred between 1988 and 2016 at a large university tertiary medical center. Women with multiple gestations and those lacking prenatal care were excluded from the analysis. Results: During the study period, 252,542 women delivered at the Soroka University Medical Center and met the inclusion criteria. Of these, 583 (0.23%) were diagnosed with OASIS. Women with OASIS were more likely to be younger, nulliparous, with suspected fetal macrosomia, had higher rates of labor induction and vacuum extraction delivery, higher rates of conceiving after infertility treatments, more advanced gestational age at delivery, higher mean birth weight, higher rates of post-partum hemorrhage and need for blood transfusions. Use of epidural analgesia during pregnancy was significantly high among the OASIS group. Rates of episiotomy were not significantly different between the groups. Using a multimodal logistic regression model, after controlling for vacuum delivery, large for gestational age, nulliparity, gestational age, ethnicity, maternal age, induction of labor, fertility treatments, non-reassuring fetal heart rate and non-progressive second stage of labor, epidural analgesia was found to be significantly associated with OASIS. Conclusion: Epidural analgesia was found to be an independent risk factor for OASIS in our population.