Multiple sclerosis is a common autoimmune and neurodegenerative disease of the central nervous system in women of reproductive age. The average age of onset is around 30 years. A few decades ago, women with multiple sclerosis were often advised to avoid pregnancy, but this has changed. Discontinuation of treatment due to pregnancy is often associated with clinical and radiological progression of multiple sclerosis. According to current expert recommendations, if a patient presents with highly active multiple sclerosis, continuation of treatment with natalizumab may be considered even during pregnancy. Treatment can be continued until 30–34 weeks of gestation and resumed as soon as possible after delivery, 2–3 weeks after childbirth or 8–12 weeks after the last infusion, to reduce the risk of disease reactivation. The dosing interval should be extended to 6 weeks. Cases of mild to moderate transient thrombocytopenia and anaemia have been reported in infants born to mothers exposed to natalizumab in the third trimester of pregnancy. Haematological abnormalities have been shown to normalise within 4 months after birth in most infants. This article presents the case of a patient with multiple sclerosis who has been successfully treated with natalizumab for several years and decided to continue her treatment during pregnancy, with an emphasis on the impact of the drug on the newborn’s laboratory parameters.