New findings suggest that disease-modifying therapy management during pregnancy, in women with multiple sclerosis, can significantly increase the relapse rate, highlighting the importance of careful therapeutic planning before pregnancy.

In women with MS, DMT management during pregnancy may affect relapse risk. French researchers set out to estimate this effect of DMT management during pregnancy on MS relapse rate and compare different therapeutic strategies.

This was a multicenter retrospective cohort study using data from January 1990 to December 2023, extracted in December 2023 from the French MS registry. The 52,955 women in the registry included pregnancies identified through childbirths in patients with relapsing-onset MS. They were monitored for at least 18 months before delivery and nine months after. Pregnancies occurring less than 18 months apart or with missing month of birth were excluded.

Mediation analysis was used to estimate the total, direct, and indirect (mediated by DMT management) effects of pregnancy. Different therapeutic strategies were compared: DMT interruption, switching to or maintaining interferon β or glatiramer acetate, switching to or maintaining natalizumab until the third trimester, and switching to or maintaining intravenous anti-CD20 and interrupting it three months before conception. The primary outcome was the annualized relapse rate during the preconception, gestation, and postpartum periods. 

Researchers included 6341 pregnancies occurring in 4998 women. DMT management during pregnancy significantly increased ARR during gestation and postpartum periods. This led to a deleterious total effect of pregnancy on ARR, particularly in women receiving natalizumab before pregnancy with prolonged interruption, and in women receiving fingolimod. Compared to DMT interruption, anti-CD20 strategy was the most effective, followed by the natalizumab strategy with short interruption, whereas interferon β and glatiramer acetate strategies were less effective.

The results were published in the journal JAMA Neurology.