July 14, 2014

Canadian researchers investigate the impact of pregnancy on the course of relapsing-remitting MS


Relapsing-remitting MS (RRMS) is typically diagnosed between the ages of 15 to 40, during the family building years. It is therefore important that information pertaining to how RRMS could affect pregnancy, and vice versa, is available. Several studies have investigated this relationship, resulting in the development of competing theories. Pregnancy was originally believed to negatively affect the course of disease. More recently, however, it was shown that pregnancy may have a positive impact on RRMS. The studies that specifically sought to address these opposing ideas were limited by small sample sizes, interpretation bias, and inability to assess the long-term consequences of pregnancy in MS.

One study published in Annals of Epidemiology, set out to provide new evidence regarding the long-term impact of pregnancy on the rate of relapse, progression to irreversible disability, and transition to secondary progressive MS (SPMS) in people with RRMS.

The Study:

Dr. Igor Karp and colleagues, including MS Society endMS Summer Studentship recipient Alexandra Manganas, from Université de Montréal examined medical record data from females with RRMS between the ages of 15 and 50. They were followed from 1977 to 2010 at the Notre-Dame Hospital Multiple Sclerosis Clinic in Montreal. Demographic, lifestyle, and clinical information was collected. A retrospective cohort study was done, meaning that researchers looked back at events that have already taken place. The women analyzed fell either into the nonpregnant group, meaning at the time of entry into the clinic they were not pregnant and data on their disease course was analyzed from that point on, or the pregnant group, meaning at some point while in the clinic they became pregnant and data on their disease course was analyzed from that point on.

The research team assessed the impact of pregnancy relapse rate, transition to secondary progressive MS (SPMS), and progression to irreversible disability. Events that represented termination of follow-up included reaching one of the above outcomes, being lost to follow-up, transition to SPMS, onset of a second pregnancy, abortion, or end of the study period.


In the group of pregnant women, 300 relapses, 15 transitions to SPMS, and 11 progressions to irreversible disability were recorded. The nonpregnant group experienced 787 relapses, 27 SPMS transitions, and 34 progressions. These findings led the researchers to suggest that pregnancy may improve the short-term course of RRMS when considering rates of relapse and slower progression of the disease. When considering the transition from RRMS to SPMS, data from this study showed no difference between the pregnant and nonpregnant groups in terms of transition to SPMS in the short-term, and suggest that pregnancy may actually increase the risk of transition in the long-term. It must be noted that this link was weak with a low number of recorded events, and thus did not have the same support as the other findings.


Overall the study reports a milder disease course in the group of women with RRMS who were pregnant during the study period. Although the pregnant group experienced less relapses and were slower to progress to irreversible disability, these effects appeared to sustain for only the first several years. The course of illness appeared to be more similar among the two groups over the long-term. Researchers suggest that this may be a result of the difference influences pregnancy can have on the inflammatory component of MS versus the neurodegenerative component of MS.

While the results from this study add to the body of data regarding pregnancy in MS, further long-term research needs to be done in order to validate the findings, as implications beyond a 10-year time period remain unclear.


Karp I et al. Does pregnancy alter the long-term course of multiple sclerosis? Annals of Epidemiology 2014 July; 24(7): 504-508.