To determine the difference in disease activity during pregnancy associated with interferon-β (INF-β) discontinuation before or after conception in women with multiple sclerosis (MS).

In disease modifying therapy unexposed pregnancies of MS-patients, relapse rate decreases significantly during pregnancy, followed by an increase in the first 16 weeks postpartum, but little is known about the relapse pattern and the associated use of steroids in IFN-β-exposed pregnancies

Pregnancies were prospectively collected in the German MS and pregnancy registry up to April 2019. Pregnancies with a duration of at least 22 gestational weeks and IFN-β treatment 12 months prior to conception were compared in two groups: preLMP(last menstrual period)-group stopping IFN-β between 365 and 1 day before LMP and postLMP-group stopping IFN-β in first trimester.

We identified 605 (172 preLMP-group, 433 postLMP-group) pregnancies. Between groups, there were no differences in age at conception, duration of INF-β treatment duration, mobility limitation and annualized relapse rate prior to pregnancy. Median follow up time post-partum was 23.92 (0.56-93) months. 99 of 605 women (16.4%) had at least one relapse during pregnancy, 39 (22.67%) in preLMP-group and 60 (13.86%) in postLMP-group. Less women in postLMP-group experienced at least one relapse in pregnancy (OR=0.54, CI [0.34-0.88], p=0.0118). Corticosteroid use did not differ significantly between groups (p=0.815). 618 infants were born (13 twin pregnancies). Preterm births differed significantly between groups, with more preterm births in the preLMP-group (27 (15.16%) in preLMP-group and 37 (8.41%) in postLMP-group; OR 2.01,CI[1.14 - 3.52], p= 0.0144). No stillbirth was observed.

IFN-β treatment should not be stopped prior to pregnancy.  At the time of the meeting, updated analysis will be presented.