The purpose was to examine the impact of pregnancy on the rates of relapses, progression to irreversible disability, and transition to secondary progressive multiple sclerosis (SPMS) in patients with relapsing-remitting multiple sclerosis (RRMS).
We retrospectively followed two subcohorts of women with RRMS: pregnant (n=254) and non-pregnant (n=423). We obtained data on demographic, life-style, and clinical characteristics from patient records. Poisson and logistic regressions estimated the rate ratios (RR) associated with pregnancy as a function of time. Confounding was controlled by propensity-score adjustment, and post-baseline selection bias was controlled by inverse probability weighting.
In the pregnant and non-pregnant subcohorts, respectively, 300 and 787 relapses, 15 and 27 transitions to SPMS, and 11 and 34 progressions to irreversible disability were documented. Adjusted RRs (95% confidence intervals) shortly after baseline were 0.67 (0.49; 0.92) for relapses, 0.16 (0.03; 0.79) for irreversible disability, and 1.25 (0.39; 3.96) for SPMS. The corresponding estimates at 5 and 10 years were, respectively, 1.04 (0.72; 1.52), 0.82 (0.36; 1.88), and 2.33 (1.03; 5.26) and 1.62 (0.84; 3.14), 4.14 (0.89; 19.22), and 4.33 (1.10; 16.99).
Pregnancy likely ameliorates the short-term course of RRMS in terms of the rates of relapses and progression to irreversible disability. Over the long term it appears to have no material impact on these outcomes, and might in fact accelerate the rate of transition to SPMS.