Safety of breastfeeding under monoclonal antibodies in the offspring of mothers with multiple sclerosis or neuromyelitis optica spectrum disorder.

Women with multiple sclerosis (MS) or neuromyelitis optica spectrum disorder (NMOSD) and highly active disease may benefit from early post partum reinitiation of disease-modifying therapy (DMT), but safety data to monoclonal antibody (mAb) use while breastfeeding are limited. This study examined infant development and health following potential mAb exposure during breastfeeding. A prospective monocentric cohort study of infants, born in 2013-2022, in the German MS and Pregnancy Registry, followed up 6-36 months post partum via telephone interviews. 183 infants breastfed during maternal mAb therapy (mAb use during breastfeeding (mAb-BF)) were matched 1:1 (DMT pregnancy exposure) to infants of DMT-na ve mothers (no-DMT-BF). Primary outcomes included developmental delay, systemic antibiotic use, hospitalisation, severe infection and growth. Adjusted regression models estimated the beta coefficient, OR or rate ratio with 95% CI. The study included 366 infants. Among 183 mAb-BF infants, most were breastfed on natalizumab (n=125), followed by ocrelizumab (n=34), rituximab (n=11) and ofatumumab (n=10); three had multiple exposures. Developmental delays occurred in 8.2% mAb-BF and in 7.1% no-DMT-BF infants (p=0.844). A comparable number of infants used a systemic antibiotic (n=33/183, 18.0% vs n=29/183, 15.8%; p=0.676), were hospitalised (n=18/183, 9.8% vs 19/183, 10.4%; p=1.000) or had a severe infection (n=14/183, 7.7% vs n=13/183, 7.1%; p=1.000). The physical growth and adjusted model outcomes were also similar. The results indicate that infants of mothers with neuroimmunological diseases, breastfed under mAbs, did not experience negative consequences for their development and health within the initial 6-36 months of life. This may encourage mothers with highly active disease to breastfeed.