Multiple sclerosis often occurs in young women, and the effect of pregnancy on the disease is poorly understood. We studied 254 women with multiple sclerosis during 269 pregnancies in 12 European countries. The women were followed during their pregnancies and for up to 12 months after delivery to determine the rate of relapse per trimester and the score on the Kurtzke Expanded Disability Status Scale (range, 0 to 10, with higher scores indicating more severe disability). The relapse rate in each trimester was compared with the rate during the year before the pregnancy. The effects of epidural analgesia and breast-feeding on the frequency of relapse during the first three months post partum and the disability score at 12 months post partum were also determined.

The mean (±SD) rate of relapse was 0.7±0.9 per woman per year in the year before pregnancy; it was 0.5±1.3 during the first trimester (P=0.03 for the comparison with the rate before pregnancy), 0.6±1.6 during the second trimester (P=0.17), and 0.2±1.0 during the third (P<0.001). The rate increased to 1.2±2.0 during the first three months post partum (P<0.001) and then returned to the prepregnancy rate. The mean Kurtzke disability score worsened by 0.7 point during 33 months of follow-up, with no apparent acceleration during the postpartum period. Neither breast-feeding nor epidural analgesia had an adverse effect on the rate of relapse or on the progression of disability in multiple sclerosis.

In women with multiple sclerosis, the rate of relapse declines during pregnancy, especially in the third trimester, and increases during the first three months post partum before returning to the prepregnancy rate.