Maternal and fetal risks of natalizumab exposure in utero

Multiple sclerosis (MS) typically presents in young adulthood, often at a time when decisions about reproduction have not been made yet. Although some individuals with MS will choose not to have children for MS-related reasons,¹ many others will choose to do so. For women, this raises particular concerns. Women with MS are slightly more likely to deliver infants who are small for gestational age, but maternal MS is not associated with a greater risk of birth defects.² During the third trimester of pregnancy, annualized relapse rates decrease, followed by an increased relapse risk particularly in the first 3 months of the postpartum period.³ Consistent with this observation, new, enlarging, or gadolinium-enhancing lesions are often detected postpartum.⁴ Disease activity gradually returns to prepartum levels, and no long-term adverse effects of pregnancy on disease progression have been identified.⁵ In the modern therapeutic era, women with MS and their physicians face sometimes challenging decisions regarding disease-modifying therapy (DMT) and how this will affect maternal and fetal health. Although use of injectable DMTs prepartum does not appear to alter the aforementioned pattern of disease activity in the third trimester or postpartum,⁶ this may not be the case for more effective therapies, such as natalizumab, which are associated with rebound disease activity when they are withdrawn.⁷