To evaluate the impact of continuing Natalizumab during pregnancy on relapse risk and maternal-fetal outcomes in MS patients and determine the optimal duration of therapy, considering the relative immune protection in the third trimester.

Natalizumab is an effective therapy for relapsing MS, but its use during pregnancy raises concerns about fetal safety and maternal relapse. The third trimester provides relative immune protection, potentially reducing the need for continuous treatment. This study evaluates the impact of discontinuing Natalizumab before the third trimester on relapse risk. 

Thirteen pregnant women with relapsing MS continued Natalizumab until the second trimester. Data collected included age, disease duration, prior DMTs, gestational age at discontinuation, EDSS scores (pre-pregnancy, post-pregnancy, and 6 months postpartum), delivery method, breastfeeding status, and postpartum MRI results. Relapse rates were tracked during pregnancy and postpartum.

All thirteen women gave birth to healthy babies. Four (30.76%) experienced peri-delivery relapses: two during pregnancy, one three months postpartum, and one developed a new lesion on postpartum MRI but remained asymptomatic. Previous studies show higher relapse rates when Natalizumab is stopped before pregnancy or in the first trimester. The lower relapse rate in this study supports extending treatment into the second trimester to balance disease control and fetal safety. 

Discontinuation of Natalizumab in the second trimester appears safe for maternal and fetal outcomes, with low relapse rates overall. However, the relatively high observed relapse rate was likely due to early discontinuation. This suggests that extending Natalizumab use further into the second trimester may provide better relapse prevention while still limiting fetal drug exposure, which is highest in the third trimester. Additionally, patients who relapsed had significantly higher pre-pregnancy EDSS scores compared to those without relapse, highlighting the role of baseline disability in relapse risk. Further studies are needed to refine treatment strategies in this population.