Month of birth has been associated with susceptibility to MS. It has been suggested that exposure to vitamin D, via sunlight may account for this difference that is having an influence in the womb. This study suggests that smoking may also be another factor. that could be a feature. Saying don’t smoke when pregant. How and what this is doing is unknown
Mueller BA, Nelson JL, Newcomb PA. Intrauterine environment and multiple sclerosis: a population- based case-control study. Mult Scler. 2012 May 8. [Epub ahead of print]
Background: Associations of several autoimmune disorders with intrauterine and early life exposures have been reported.
Objective: We used population-based linked hospital discharge-birth records data to explore maternal, prenatal, and infant characteristics in relation to MS-related hospitalization among Washington State residents.
Methods: 272 cases hospitalized for MS during 1988-2008 and 2720 birth record controls were identified from linked hospital discharge-birth certificate data. Exposure information from their birth records were compared in a population-based case-control study to estimate adjusted odds ratios (ORs) and 95% confidence intervals (95%CIs) for associations with MS hospitalization.
Results: Most factors examined were not associated with MS. Having a mother with 3+ prior live births (OR 0.54, 95%CI 0.31-0.95) or having 3+ older siblings (OR 0.49, 95%CI 0.28-0.85) were negatively associated. Maternal prenatal smoking (OR 3.09, 95%CI 1.22-7.84) was positively associated.
Conclusion: Transplacental exposure to smoke constituents including chemicals affecting myelin may help explain any association with maternal prenatal smoking; however, we were unable to assess childhood or adult smoke exposures which may also account at least partly for this effect. The negative associations observed with greater maternal parity and number of siblings are consistent with some other studies. Reasons for these associations may involve various pathways.