Pregnancy outcomes amongst multiple sclerosis females with third trimester natalizumab use

Background: Natalizumab, a monoclonal antibody directed against alpha-4-integrin, is an efficacious treatment used in Multiple Sclerosis (MS). Use in early pregnancy is safe but information in the third trimester is limited. Ceasing natalizumab is often associated with an increased risk in MS relapse and in some instances natalizumab continuation during pregnancy may be required. However natalizumab crosses the placenta in late pregnancy and has been associated with hematological abnormalities. We present clinical and hematological outcome data of newborns from a series of MS patients who received natalizumab during their second and third pregnancy trimesters. We describe possible methods to mitigate risks to the fetus. Methods: Retrospective chart review of 15 births from mothers receiving natalizumab throughout pregnancy. Results: Thirteen mothers with third-trimester exposure to natalizumab were identified. Median age at conception was 34 years (26-40) and median disease duration was 53.5 months (11-204). The 13 mothers gave birth to 15 newborns (2 mothers each with 2 individual births), median (SD) birth weight was 2778 gs (2100-3790). Congenital or laboratory abnormalities were identified in 5 which included anemia (n = 2) and thrombocytopenia (n = 3). Conclusions: Complications following natalizumab administration during the second and third trimester of pregnancy occurred in 33% of newborns. However, did not result in mortality or morbidity. Dose alterations during the third trimester, pre-delivery umbilical cord sampling and IVIG administration may reduce hematological effects on newborns. Prospective studies with larger numbers of patients are required to provide further evidence regarding the safety of Natalizumab use in pregnancy.