Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating, and neurodegenerative disease predominantly affecting young women during the reproductive years. Many patients who become mothers wish to breastfeed, but both mothers with MS and their healthcare specialists may have concerns about the disease outbreak after delivery leading to severe disability that could complicate care of a newborn. Pregnancy, mainly in the third trimester, is favorable for the MS course regarding clinical outcomes, but the postpartum period brings higher risk of relapses and disease progression. The entire period of pregnancy may not confer sufficient protection against this risk as some trials have yielded postpartum evidence of disease progression at the subclinical level. This evidence includes increased T2 lesion volume, accelerated brain volume loss (Uher et al., 2022), and new T2 and/or gadolinium enhancing lesions (Anderson et al., 2021) compared with the pre-pregnancy period. Increased serum light-chain neurofilament values have been reported in pregnant and postpartum MS patients compared with nonpregnant or non-postpartum patients with MS and with patients who did not discontinue disease modifying treatment (DMT) during pregnancy (Yaldizli, 2020). Current treatment options for MS include several drugs with different modes of action. Until recently, use of DMTs during breastfeeding was not recommended and considered potentially harmful. Furthermore, many women considering pregnancy or who are already pregnant share profound uncertainties and specific concerns about using specific DMTs during pregnancy and breastfeeding (Rezaallah et al., 2019). Evidence is overwhelming, that both babies and mothers benefit from breastfeeding, which should thus be promoted and protected. Numerous comprehensive studies have summarized the benefits of breastfeeding (Victora et al., 2016; Ip et al., 2007; Horta and Victora, 2013; Bowatte et al., 2015; Horta et al., 2015; Brenton, 2017; Prentice, 2022; Chowdhury et al., 2015).

Information about the impact of breastfeeding on the long-term course of MS is routinely collected from clinical trials or registries focused on one DMT used during at least part of a pregnancy or during breastfeeding. Here, we used real-world data collected prospectively from the national multiple sclerosis patient registry ReMuS established in 2013 in the Czech Republic. Data for this registry are collected from the 15 specialized MS centers in the country.

The objectives of our study were as follows: (a) to assess factors associated with initiation of breastfeeding in Czech MS patients, (b) to provide information about the impact of breastfeeding on the disease course in Czech women with MS, (c) to evaluate the assumption that breastfeeding is not harmful for the disease course in MS, even if patients use no DMTs, and (d) to compare the MS disease course in breastfeeding women with that in women who did not breastfeed and restarted a DMT within 3 months after delivery.