Disease-modifying therapy during pregnancy and postpartum relapse activity in women with multiple sclerosis undergoing assisted reproductive technology treatment: a nationwide cohort study.

Background: Evidence is scarce concerning the impact on postpartum relapse activity of disease-modifying therapy (DMT) use during pregnancy after assisted reproductive technology (ART) treatment. We investigated relapse activity before pregnancy, during pregnancy and 3 and 12 months postpartum overall and according to DMT exposure during pregnancy. Methods: Women with relapsing-remitting multiple sclerosis (MS) from the Danish MS Registry who gave birth after ART from 1995 to 2018 were eligible for inclusion. Annualised relapse rate (ARR) before pregnancy, during pregnancy and postpartum was evaluated using a negative binomial regression model with relapse count as the dependent variable overall and according to DMT exposure during pregnancy. Logistic regression was used to identify predictors of being relapse-free 12 months postpartum. Results: A total of 111 women, median age 32 years (IQR: 29-35), were included. Overall, ARR (95% CI) was 0.14 (0.08 to 0.24) before pregnancy, 0.13 (0.07 to 0.25) during pregnancy and 0.33 (0.17 to 0.61) 3 months postpartum; rate ratio difference between before pregnancy and postpartum was 2.42 (1.03 to 5.67), and between during pregnancy and postpartum was 2.46 (1.18 to 5.13). Age ≥35 years and no DMT exposure before pregnancy were predictors of being relapse-free 12 months postpartum. Conclusions: Relapse activity was more than two times higher 3 months postpartum than before and during pregnancy. Stratified for DMT exposure during pregnancy, rate ratios were similar and did not reach statistical significance. Postpartum relapse activity more than doubled from both low ARR (unexposed to DMT during pregnancy) and higher ARR (exposed to DMT during pregnancy) pre-pregnancy.