Association between the month of birth and Multiple Sclerosis; a meta-analysis

Background Knowledge regarding true birth-month effect on Multiple Sclerosis (MS) risk has important effect on the adoption of preventive strategies. In this meta-analysis we assessed the Association between month of birth and MS, during 2000-2020. Methods: In this systematic review, an extensive search was performed on the scientific databases including PubMed, SCOPUS and Web of Science. They were electronically searched using detailed search strategy to December 2020. Reviewing and extracting the data were done by two independent authors. I² statistics were used to assess the heterogeneity in the included studies. Depending amount of heterogeneity random or fix effect model was used to estimate the pooled OR. Results: In the initial search we enrolled 93 records according to search strategy. However, 15 articles, with 181602 total subjects, were finally included in the Meta-analysis. According to results from pooled meta-analysis the excess risk of MS by birth months observed in April and June was 1.03 (1.00 – 1.06), and 1.02 (1.00 – 1.05), respectively; while the lower risks of MS by birth months were attributed to January and November the expected MS birth odds ratio of which has been 0.98 (0.96 – 0.99), and 0.96 (0.93 – 1.01), respectively. Conclusion: Our meta-analysis showed that Month of birth has a significant effect on subsequent MS risk. This can be due to the amount of ultraviolet light exposure in the third trimester of pregnancy. Increased vitamin D intake from supplements under conditions of limited exposure to sunlight can be effective in preventing MS.