Historically, disease activity diminished during pregnancy in women with relapsing-remitting MS. Today, women with high disease activity are more likely to attempt pregnancy due to the disease control that new therapies offer. But disease activity during pregnancy in the modern day remains understudied.
Describe disease activity in a modern pregnancy cohort, grouped by preconception disease-modifying therapy (DMT) class; determine the predictors of relapse during pregnancy.
Data were obtained from the MSBase Registry. Term/preterm pregnancies conceived from 2011-2019 were included. DMT were classed by low, moderate and high-efficacy. Annualized relapse rates (ARR) were calculated for each pregnancy trimester and 12 months either side. Predictors of relapse during pregnancy were determined using clustered logistic regression.
We included 1640 pregnancies from 1452 women. DMT used in the year before conception were none (n=346), low (n=845), moderate (n=207) and high-efficacy (n=242). Most common DMT in each class was interferon-beta (n=597), fingolimod (n=147) and natalizumab (n=219) for low, moderate and high-efficacy respectively. Conception EDSS ≥2 was more common in higher efficacy DMT groups (high: 41.3%; moderate 28.5%; low 22.4%; none 20.2%). For low-efficacy and no DMT groups, ARR fell through pregnancy. ARR of the moderate-efficacy group increased in the 1st pregnancy trimester (0.55 [95% CI 0.36-0.80] vs 0.14 [95% CI 0.10-0.21] on low-efficacy), then decreased to a trough in the third. Conversely, ARR steadily increased throughout pregnancy for those on high-efficacy DMT (3rd trimester: 0.42 [95% CI 0.25-0.66] vs 0.12 [95% CI 0.07-0.19] on low-efficacy). Higher efficacy DMT groups were associated with higher ARR in the early postpartum period (high: 0.84 [95% CI 0.62-1.1]; moderate: 0.90 [95% CI 0.65-1.2]; low: 0.47 [95% CI 0.38-0.58]). Preconception use of high and moderate-efficacy DMT and higher preconception ARR were predictors of relapse in pregnancy. But, continuation of high-efficacy DMT into pregnancy was protective against relapse (odds ratio 0.80 [95% CI 0.68-0.94]). Age ≥35 years was associated with reduced odds of relapse.
Women with RRMS treated with moderate or high-efficacy DMT are at greater risk of relapse during pregnancy. Careful pregnancy management, and use of long-acting high-efficacy DMT preconception, or continuing natalizumab into pregnancy, may prevent relapse in pregnancy.