The relapse rate of multiple sclerosis changes during pregnancy: a cohort study

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To evaluate the influence of pregnancy and puerperium on the relapse rate of multiple sclerosis (MS).


We determined retrospectively the yearly mean relapse rate (MRR) during pregnancies occurring in the course of relapsing–remitting MS. We compared the MRR of pregnancy-time with that of non-pregnancy time by paired t-test. Relative risk (RR) of relapses during the pregnancy-time was also compared with that of non-pregnancy time by χ2 analysis and 95% confidence intervals.


From a population of 351 women affected by clinically definite MS, only 70 reported pregnancies during their relapsing–remitting phase of MS for a total of 98 pregnancies. Both MRR (P = 0.006) and RR (RR = 0.63, 95% CI = 0.40–0.94) decreased during the three trimesters of pregnancy. RR increased in the first 3 months of puerperium, although this was not statistically significant (RR = 1.36, 95% CI = 0.79–2.20).


Our study confirms that in MS the relapse rate decreases throughout pregnancy and increases during puerperium. This suggests a complex interplay between hormonal and immune factors.

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