A woman had received natalizumab during pregnancy every 6 weeks. The baby was born at 37 + 5/7 weeks of gestation. The baby’s weight was 2,915 g, the APGAR score at 1 and 5 min was 9/10; globally, the newborn underwent a regular adaptation to extra-uterine life. Blood exams performed after birth revealed a low-moderate anemia (Hb: 10.9 g/dL; hematocrit 34.1%). Blood samples collected at 40 days of life showed the Hb was 8 g/dL and the hematocrit was 23.5%. The baby received therapy with erythropoietin (EPO) and at 4 months of life, the Hb was 12 g/dL and the hematocrit was 37.4% Here, EPO is linked to anemia (phenotype).