A recent study (Ponsonby et al., 2012) indicated a robust, cumulative, and beneficial effect of pregnancy and childbirth on the risk of a first clinical demyelinating event (CDE) in women, including a permanent additive effect from each birth. Increased numbers of pregnancies and deliveries were associated with decreasing risk of a first clinical demyelinating event. The authors postulate that if these associations are shown to be causal, they could help explain the increasing female to male ratio in MS (Alonso & Hernan, 2008) in a time when women are getting pregnant at a later age and having fewer children. No association was found between the number of offspring and the risk of a first demyelinating event in men.
Pregnancy is characterized by a down-regulation of cellular immune responses and the presence of potentially neuroprotective hormones, both of which protect the developing fetus. The combined anti-inflammatory and neuroprotective effects of pregnancy appear to have a positive impact on MS as well (Voskuhl R & Giesser B 2011. Gender and reproductive issues. In Giesser (ed.) Primer on Multiple Sclerosis, NY: Oxford University Press).
The risk of relapse drops over the nine months of pregnancy (with the risk being lowest in the third trimester), rises significantly in the three-six months postpartum, and then returns to the woman’s pre-pregnancy rate. The more active a woman’s disease is during pregnancy and the year prior, the higher her risk of postpartum relapse (Vukusic et al., 2004).
Women who become pregnant after the onset of MS may have a decreased risk of transitioning from relapsing-remitting to secondary-progressive MS as compared to women who do not become pregnant (Runmaker & Andersen, 1995).
Available data suggest that pregnancy in healthy women has no long-lasting effects with regard to reducing their risk of developing MS (Voskuhl R & Giesser B 2011. Gender and reproductive issues. In Giesser (ed.) Primer on Multiple Sclerosis, NY: Oxford University Press).