Pregnancy and fetal outcomes following natalizumab exposure in pregnancy. A prospective, controlled observational study

Background: Safety data on first-trimester natalizumab exposure are scarce, as natalizumab is usuallywithdrawn three months before pregnancy.Objective: The objective of this paper is to investigate the fetal safety of exposure to natalizumab (Tysabri) during the first trimester of pregnancy using disease-matched (DM) and healthy control (HC) comparisongroups.Methods: A total of 101 German women with RRMS exposed to natalizumab during the first trimester ofpregnancy were identified. Birth outcomes in the exposed group were compared to a DM group (N = 78)with or without exposure to other disease-modifying drugs, and an HC group (N = 97).Results: A total of 77, 69 and 92 live births occurred in the Exposed, DM and HC groups, respectively.The rates of major malformations (p = 0.67), low birth weight (<2500 grams) (p = 1.0) and prematurebirth (p = 0.37) did not differ among groups. Higher miscarriage rates (p = 0.002) and lower birth weights(p = 0.001) occurred among the Exposed and DM groups, as compared to the HC; however, there was nosignificant difference between the Exposed and DM groups.Conclusion: Exposure to natalizumab in early pregnancy does not appear to increase the risk of adversepregnancy outcomes in comparison to a DM group not exposed to natalizumab.