Oral Concurrent Session 5 – Clinical Obstetrics

Objective: The C/SOAP trial (late 2016) showed that perioperative azithromycin for cesarean birth after labor reduces postpartum infection.We sought to analyze the uptake and effect of azithromycin on postpartum infection in a nationwide cohort outside of a clinical trial.Study Design: This was a difference-in-differences (DID) analysis (2013-2024) using the nationwide Epic Cosmos platform.Laboring persons without IAI who gave birth to a liveborn singleton at 24-43 weeks were included.The primary exposure was perioperative azithromycin.In the DID design, cesarean births (treatment group) were compared to vaginal births (control group); the pre-period was 2013-2016, and the post-period 2017-2024.The primary outcome, adapted from the C/SOAP trial, was a composite of endometritis, wound infection, or other infection within 6 weeks, identified by ICD codes.The DID analysis used patient-level linear regression, adjusting for age, parity, delivery BMI, diabetes, prior cesarean birth, gestational age, ROM ≥ 18 hours, and reaching the second stage.Results: The cohort included 1,636,152 individuals; 212,030 (13.0%) delivered by cesarean.Azithromycin was administered to 73,969 (34.9%) of the cesarean and 442 (0.03%) of the vaginal births.There was a rapid increase in use among cesarean births after 2016, from 2.1% in 2013 to 61.2% in 2024 (Figure 1).There was no increase in use among vaginal deliveries.Among cesarean births, 6.8% who received azithromycin and 8.0% of those who did not developed an infectious complication (p < 0.001).The rate of infection increased from 1.9% to 2.6% among vaginal births and decreased from 8.6% to 7.4% among cesarean births between the two periods (Figure 2).In the adjusted DID analysis, azithromycin reduced the incidence of infectious complications by -2.1 [-2.3, -1.9] percentage points (∼22% reduction).Conclusion: In a nationwide cohort, there was rapid uptake of azithromycin administration after cesarean birth, which decreased postpartum infectious complications.These findings demonstrate external validity of the C/SOAP trial findings in contemporary obstetric practice.