Impact of pregnancy on conversion to clinically isolated syndrome in a radiologically isolated syndrome cohort

Background: In multiple sclerosis (MS), the relapse rate declines during pregnancy and increases during the first three months post-partum before returning to the pre-pregnancy rate. It is unknown whether pregnancy impacts the risk of clinical conversion in those within the presymptomatic period. Objectives: We investigate the impact of pregnancy on developing a clinical event in women diagnosed with radiologically isolated syndrome (RIS). Methods: All women with RIS underwent clinical and radiological assessments as part of an observational, prospective, longitudinal study. Clinical and MRI outcomes were analyzed during and after pregnancy. Subjects who became pregnant were compared with an age-matched female RIS group who did not become pregnant during the same follow-up period. Results: A total of 60 women with RIS were followed for up to seven years. Among them, seven became pregnant and were compared with 53 age-matched control women with RIS who did not become pregnant during the observation period. A significantly shorter time of conversion to the first neurological event was observed in the pregnant group [15.3 months (10-18)] compared with the non-pregnant controls [35.7 months (8-76)], yielding an absolute difference of 20.4 months (p<0.05). The mean (SD) number of active lesions on a subsequent brain MRI scan was significantly higher in the pregnant group [3.2 (+/- 1.7)] compared with the control group [1.8 (+/- 0.6)]. Conclusions: The risk for clinical conversion from RIS to a clinical event and new MRI disease activity seems to be influenced by pregnancy. Pregnancy related physiological changes could operate as early as the presymptomatic period in patients with MS.