Impact of interferon beta exposure on birth outcome and child development – Results from the post-authorisation safety study PRIMA

•4-year follow-up of 192 infants exposed to interferon β during pregnancy or lactation.•Out of 158 breastfed infants, 112 (70.9%) were breastfed exclusively until month 5.•Child anamnesis and examinations during check-ups were inconspicuous up to 48 months.•No adverse effects on intrauterine growth and child development over the study period.•These real-world data corroborate German and Scandinavian registry data.