DMT exposure during pregnancy and postpartum decision making: data from the UK MS pregnancy register

<h3>Background</h3> Disease-specific pregnancy registers collect real-world data to substantially inform care for people living with chronic diseases. The UK MS Pregnancy Register launched in July 2021. <h3>Methods</h3> Data are collected directly from people living with MS at specific timepoints during pregnancy and the postpartum period via structured questionnaire. Data up to December 2023 is presented. <h3>Results</h3> A total of 223 pregnancies were included. Mean maternal age at registration was 34.4 years (range 20.8-45.5), mean age at diagnosis 29.1 years (16.0-44.0) and median EDSS 2.0 (0-6.5). 45% participants registered in the first trimester of pregnancy. 89% had ever taken DMT (8% induction therapies), and 48% continued DMT into pregnancy. 63% of those taking interferon, 78% of those taking glatiramer acetate and 94% of those taking natalizumab continued into pregnancy. 40% of those taking DMT at 15 weeks gestation planned to stop later in pregnancy. 6% of participants reported relapses during pregnancy or postpartum, with 53% of relapses reported as mild and the remaining 47% reported as moderate. No hospitalisations were reported following relapses. There were no preterm births, and no major congenital malformations were reported. Of those with postpartum data available, 42% reported exclusively breastfeeding at 3 months. Whilst some participants switched to mixed/formula feeding due to low milk supply, 6 participants reported that MS had influenced their breastfeeding decision; less than half cited DMT as a reason.