Parity Associated with Long-Term Disease Progression in Women with Multiple Sclerosis

Background: Pregnancy in multiple sclerosis (MS) is marked by a decrease in relapse activity with a corresponding rebound in the first months postpartum. Because MS typically occurs during childbearing years, it is important to determine the long term effect of pregnancy. Design/Methods: Subjects were part of the New York State Multiple Sclerosis Consortium registry. 1,195 parous and 328 nulliparous women with clinically definite MS age 45 or older were analyzed to determine time to a disability milestone, Expanded Disability Status Scale (EDSS) 6.0. A Cox proportional hazards model was used to examine the effect of parity on time from MS disease onset to EDSS 6.0, adjusted for confounding factors. Results: The average disease duration for 1,523 women was 18.1 years. During a mean follow-up period of 5.6 years 23.1% of the parous group reached EDSS 6.0, compared to 26.5% of the nulliparous women. Cox survival curves between parous and nulliparous women were significantly different (HR=.68, CI=.53-.87, p=.002), with parous women showing a longer time to reach the disability outcome. Follow-up analyses stratified by MS type showed that parity remained a significant predictor of disease progression in relapsing remitting (RRMS) patients, whereas this effect was not observed within progressive subtypes. Conclusions: Our results demonstrate that parous women with RRMS take a longer time to reach a well-defined disability milestone (i.e. use of cane) compared to nulliparous women, suggesting that pregnancy may convey a long term benefit. Further research is needed to determine why pregnancy might be protective against long term MS disability progression.