The Number of Pregnancies is Associated with an Increased Risk of Rheumatoid Arthritis: Evidence from NHANES 2015–2018

Background: The association between the number of pregnancies and the risk of rheumatoid arthritis (RA) remains uncertain. The National Health and Nutrition Examination Survey (NHANES) is a nationwide health and nutrition survey program. This study endeavors to elucidate the relation of the number of pregnancies to RA using 2015– 2018 NHANES data and lay a theoretical groundwork for clinical prevention and management. Methods: Data from NHANES 2015– 2018 were analyzed, with the number of pregnancies considered as the exposure variable and RA as the outcome. Potential confounders encompassed age, race, education, blood pressure, body mass index (BMI), glycated hemoglobin (HbA1c), fasting plasma glucose (FPG), and insulin. The association of the number of pregnancies with RA was explored through weighted logistic regression (LR) and subgroup analyses. The possible nonlinear relationship of the number of pregnancies with RA risk was investigated via restricted cubic spline (RCS) models. Results: 2383 participants were encompassed, of whom 143 (3.9%) were diagnosed with RA. After adjustment for all covariates, multivariable LR analysis indicated that a higher number of pregnancies was related to an elevated RA risk (odds ratio (OR) = 1.139, 95% confidence interval (CI) = 1.020– 1.272, P = 0.023). Subgroup analyses yielded consistent results across strata. In the RCS regression model, RA risk increased in an approximately linear fashion with increasing number of pregnancies. A threshold of three pregnancies was identified, beyond which the risk of RA increased markedly. Moreover, the likelihood of developing RA increases with a greater number of pregnancies. Conclusion: A Higher number of pregnancies is related to an elevated RA risk. Notably, when the number of pregnancies exceeds three, the risk of developing RA rises significantly. Keywords: the number of pregnancies, rheumatoid arthritis, NHANES, relationship, a cross-sectional study