Multiple Sclerosis Disease Activity and Disability Following Discontinuation of Natalizumab for Pregnancy.

Importance: The magnitude of risk of pregnancy-related multiple sclerosis relapses, particularly severe relapses, following natalizumab cessation is unclear, as is whether this risk is reduced by pregnancy or other modifiable factors. Objective: To determine the association of early natalizumab withdrawal before or during pregnancy with risk of severe relapses and relapse-related disability. Design, Setting, and Participants: This prospective cohort study used data from the German Multiple Sclerosis and Pregnancy Registry, which enrolled participants between November 2006 and February 2018. Data were collected through structured telephone-administered questionnaires and review of neurologists' notes. Registry patients who stopped natalizumab treatment within the 2 years before or in the first trimester of pregnancy were included in this analysis. Data were analyzed between January and November 2021. Exposures: Cessation of natalizumab before pregnancy or until the first trimester. Main Outcomes and Measures: Severe and significant relapse-related disability was defined as at least a 2.0-point increase on the expanded disability status scale or new or worsening relapse-related ambulatory impairment. Multivariable models accounting for measures of disease severity and repeated events were used. Results: The cohort comprised 255 women with 274 pregnancies (mean [SD] age at pregnancy onset, 31.25 [4.27] years) who stopped natalizumab before pregnancy (n = 85; median time before last menstrual period, 14.29 weeks [IQR, 3.14-42.43 weeks]) or in the first trimester (n = 189). During pregnancy and the postpartum year, relapses were reported in 183 pregnancies (66.78%), severe relapses in 44 pregnancies (16.05%), and potentially life-threatening relapses in 3 pregnancies (1.10%). One year post partum, significant relapse-related disability was accrued in 29 pregnancies (10.58%). Relapses during pregnancy (n = 109; 39.78%) and in the postpartum period (n = 135; 49.27%) were common. Pregnancy (as a time-dependent covariate) was not associated with a reduced relapse risk (adjusted HR, 0.90; 95% CI, 0.64-1.27). Neither exclusive breastfeeding (adjusted HR, 1.34; 95% CI, 0.86-2.10) nor restarting natalizumab within 4 weeks post partum (adjusted HR, 1.06; 95% CI, 0.48-2.36) were associated with a reduced risk of early postpartum relapses 6 months after delivery. However, the relapse rate ratio during 12 months post partum was lower (0.49; 95% CI, 0.28-0.86) when natalizumab was restarted in the first 4 weeks after birth. Conclusions and Relevance: This cohort study's finding suggest that 10% of women may retain clinically meaningful disability from pregnancy-related natalizumab cessation relapses 1 year post partum. This information should be shared with women on natalizumab who desire pregnancy to weigh the high risk of pregnancy-related relapses and disability to the partly uncertain risks of continuing natalizumab throughout pregnancy or switching to depleting agents before conception.