Pregnancy and natalizumab: results of an observational study in 35 accidental pregnancies during natalizumab treatment

Background: Natalizumab, a therapeutic monoclonal antibody approved for the treatment of relapsing-remitting multiple sclerosis (RRMS), is recommended to be withdrawn 3 months prior to a planned pregnancy. Our aim was to analyse the safety and impact of natalizumab exposure on course of disease and pregnancy outcome. Objectives: Prospective follow-up of women with MS who became accidentally pregnant during natalizumab treatment in comparison with pregnancies of women with MS not exposed to disease-modifying treatments (DMT). Method: 35 women with MS who became accidentally pregnant while treated with natalizumab, and 23 women with MS who became pregnant devoid of any DMT as a control group, were chosen. Results: All pregnancies except one were followed in a prospective fashion. Of the women exposed to natalizumab during pregnancy, 29 women gave birth to 28 healthy children; one child was born with hexadactyly. Five pregnancies ended in an early miscarriage and one woman decided to undergo an elective termination of pregnancy. MS activity did not rebound during pregnancy or post partum after natalizumab was withdrawn, and no significant differences were observed when compared with the non-DMT-exposed control group. Conclusion: Our data may support the notion that an elective termination of pregnancy due to natalizumab exposure may not be necessary, but rather requires careful monitoring. Women should still be advised to stop natalizumab in the course of planned pregnancy until more data on long-term outcomes are available.