Background:No specific treatment has demonstrated its effectiveness to prevent postpartum relapses for multiple sclerosis (MS) women.Objective: To assess the effectiveness of preventive high-dose corticosteroids in the post-partum period by comparing two strategies: (1) no preventive treatment and (2) standardized preventive treatment. Methods:We selected 5 French Multiple Sclerosis centers using the same post-partum strategy for their patients -either high-dose steroids (treating centers TC) or no treatment (non-treating centers NTC). We included relapsing-remitting multiple sclerosis women who delivered between January 2007 and January 2017. Our primary outcomes were the time from delivery to first relapse, EDSS progression and MRI activity between patients of treating centers and non-treating centers, after propensityscore weighting.Results: 350 patients were included (116 from treating centers, 234 from non-treating centers). For both groups, the annualized relapse rate decreased during pregnancy (0.28 in treating centers and 0.34 in non-treating centers during the third trimester) and increased during the first post-partum trimester (0.45 and 0.69 respectively) with 11% and 14% (NS) of patients facing at least one relapse respectively. Our primary outcomes were not statistically different between both groups. Conclusion:This study provides class III evidence that systematic high-dose corticosteroids are not associated with a reduced inflammatory activity during the postpartum period in multiple sclerosis patients.

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