Pregnancy History, Oral Contraceptive Pills Consumption (OCPs), and Risk of Multiple Sclerosis: A Systematic Review and Meta-Analysis.

BACKGROUND: To estimate the pooled odds of oral contraceptive pills consumption (OCPs) use as well as pregnancy history and multiple sclerosis (MS) risk. METHODS: We systematically searched PubMed, Embase, Scopus, Web of Science, Google scholar, and gray literature including references of the references as well as conference papers. The search strategy in PubMed was ((Oral contraceptive pills) OR OCP) AND (Multiple Sclerosis OR Sclerosis, Multiple) OR Sclerosis, Disseminated) OR Disseminated Sclerosis) OR MS (Multiple Sclerosis)) OR Multiple Sclerosis, Acute Fulminating) AND (gravidity) OR (pregnancy). RESULTS: Four studies were included. The pooled odds of developing MS in women with pregnancy history compared with nulligravid women was 0.64 (95%CI = 0.53 - 0.78) (I 2 = 0, P = 0.5), which means that pregnancy reduces the risk of MS by 36%. The pooled odds of OCP consumption and risk of MS were 1.09 (95% CI = 0.67 - 1.76). By comparing the pooled odds of OCP consumption and risk of MS according to the country of the origin, we found that the pooled odds in Iranian studies was 1.03 (95% CI = 0.31 - 3.45) and the pooled OR in studies that were conducted in the United States was 1.13 (95% CI = 0.65 - 1.98), which showed that the country of the origin was not the cause of heterogeneity. CONCLUSIONS: The results of this systematic review show that pregnancy history is a protective factor for MS development, whereas OCP use has no significant effect.