Insights into risk factors of medical abortion: A Mendelian randomization study

Objective: : To explore the potential factors that contribute to the occurrence of medical abortion(MA) through a Mendelian randomization(MR) study. Design: Univariate MR(UVMR) and multivariate MR(MVMR) analyses. Setting: Genetic variants from European populations. Population or Sample: Instrumental variants for MA were obtained from FinnGen with 36,232 cases and 149,622 controls. Methods: : The inverse variance weighting method was adopted as the primary analysis. Main outcome measures: The associations of MA with household income(HI), education attainment(EA), cognitive performance(CP), risky behaviors: smoking behavior(SB), alcohol consumption(AC), and reproductive traits: age at first sexual intercourse(AFS), lifetime number of sexual partners(LNSP), age at first birth(AFB), age at last birth(ALB). Results: : In the UVMR, increasing HI, EA, AFS and AFB appeared to reduce MA risk(HI, OR=0.569, P = 7.93E-08; EA, OR=0.875, P = 6.02E-21; AFS, OR=0.439, P = 5.17E-25; AFB, OR=0.815, P = 5.46E-12), whereas SB and LNSP appeared to add to MA risk((SB, OR=1.424, P =8.32E-11; LNSP, OR=2.777, P =2.14E-11). In the MVMR, EA, SB, LNSP and AFS seems to be the predominant risk factor for MA risk with the independent effect, while HI had no effect after controlling EA(HI in model 1, OR=0.890, P = 5.78E-01). AFB functioned as mediators in the causal chain of MA risk reduction by EA, with the mediated proportion of AFS and AFB being 57.8%. Conclusions: : Our MR study demonstrated the causal potential of the associations of HI, EA, SB, LNSP, AFS and AFB with medical abortion.