Pregnancy and multiple sclerosis (the PRIMSstudy): clinical predictors of post-partum relapse

The in¯uence of pregnancy in multiple sclerosis has been a matter of controversy for a long time. The Pregnancy in Multiple Sclerosis (PRIMS) study was the ®rst large prospective study which aimed to assess the possible in¯uence of pregnancy and delivery on the clinical course of multiple sclerosis. We report here the 2-year post-partum follow-up and an analysis of clinical factors which might predict the likelihood of a relapse in the 3 months after delivery. The relapse rate in each trimester up to the end of the second year post-partum was compared with that in the pre-pregnancy year. Clinical predictors of the presence or absence of a postpartum relapse were analysed by logistic regression analysis. Using the best multivariate model, women were classi®ed as having or not having a post-partum relapse predicted, and this was compared with the observed outcome. The results showed that, compared with the pre-pregnancy year, there was a reduction in the relapse rate during pregnancy, most marked in the third trimester, and a marked increase in the ®rst 3 months after delivery. Thereafter, from the second trimester onwards and for the following 21 months, the annualized relapse rate fell slightly but did not differ signi®cantly from the relapse rate recorded in the pre-pregnancy year. Despite the increased risk for the 3 months post-partum, 72% of the women did not experience any relapse during this period. Con®rmed disability continued to progress steadily during the study period. Three indices, an increased relapse rate in the pre-pregnancy year, an increased relapse rate during pregnancy and a higher DSS (Kurtzke's Disability Status Scale) score at pregnancy onset, signi®cantly correlated with the occurrence of a postpartum relapse. Neither epidural analgesia nor breastfeeding was predictive. When comparing the predicted and observed status, however, only 72% of the women were correctly classi®ed by the multivariate model. In conclusion, the results for the second year post-partum con®rm that the relapse rate remains similar to that of the pre-pregnancy year, after an increase in the ®rst trimester following delivery. Women with greater disease activity in the year before pregnancy and during pregnancy have a higher risk of relapse in the postpartum 3 months. This is, however, not suf®cient to identify in advance women with multiple sclerosis who are more likely to relapse, especially for planning therapeutic trials aiming to prevent post-partum relapses.