Fig. 2

Selection process for mediators in the causal associations of birthweight with MI and AF. Three criteria were applied to screen for the mediators in the causal associations of birthweight with MI and AF: [1] birthweight is causally associated with the mediator; [2] the mediator has a direct causal effect on the outcome independently of birthweight; and [3] the total effect of birthweight on the outcome and the mediating effect of the mediator are in the same direction. Eventually, a total of 17 and 5 qualified mediators met all criteria and were included in the mediation analyses to quantify their individual mediating proportions in the causal associations of birthweight with MI and AF, respectively. The full MR estimates are shown in Additional file 1: Table S5, Table S7.  AF  atrial fibrillation, ApoA-I  Apolipoprotein A-I, ApoB  Apolipoprotein B, BMI  body mass index, CI  confidence interval, CKD  Chronic kidney disease, CRP  C-reactive protein, DBP  diastolic blood pressure; DHA  docosahexaenoic acid, eGFR  estimated glomerular filtration rate, HbA1c  glycated hemoglobin, HDL-C  high-density lipoprotein cholesterol, LDL-C  low-density lipoprotein cholesterol, MI  myocardial infarction, SBP  systolic blood pressure; TDI  Townsend deprivation index, UACR  urinary albumin-to-creatinine ratio; WC  Waist circumference, WHR  waist-to-hip ratio