Timing of Mifepristone Relative to Misoprostol Critical for Reducing Blood Loss and Need for Surgical Procedure for Induction of Labor in the Second Trimester [ID 2683544]

INTRODUCTION: Mifepristone is used in combination with misoprostol to facilitate inpatient induction of labor in the second trimester; however, the optimal interval of time between administration of these drugs is not known. Current practice guidelines recommend an interval of 24–48 hours. METHODS: In a single-institution retrospective chart review study, we examined whether mifepristone administration practices at that institution improved loss induction duration or adverse outcomes. This study was determined to be exempt from IRB approval. RESULTS: Among 267 loss inductions from 2018 to 2022, 54% received mifepristone. When misoprostol-alone inductions are compared to those that also received mifepristone, results demonstrate no difference in time to delivery (15.1 versus 15.9 hours; P =.62) or adverse outcomes, including blood loss greater than 1 L (8.2% versus 13.1%; P =.24) and need for operating room (OR) procedure (15.6% versus 16.6%; P =.86). Importantly, the average interval in this study between administration of mifepristone and misoprostol was 1.3 hours (median, 0.1 hours). Further analysis of those patients who received mifepristone demonstrated improved outcomes only if mifepristone was given at least 3 hours prior to misoprostol, including blood loss greater than 1 L (17.4% versus 0%; P =.0037) and need for OR procedure (21.4% versus 2.7%; P =.0088). There remained no difference in time to delivery (16.0 versus 15.8 hours; P =.94). CONCLUSION: These data demonstrate the importance of the timing of mifepristone and misoprostol administration for loss induction and strongly suggest that at least a 3-hour interval is required to improve adverse outcomes. Further prospective study is warranted to broaden the scope of these findings.