Scatterplot for two-sample Mendelian randomization analysis for the maternal effect of gestational duration on birth weight ( b , maternal effects; c , fetal effects). Each dot represents one of the gestational duration index SNPs. Effect sizes and standard errors (horizontal or vertical error bars) from the index SNPs for gestational duration derived from the maternal nontransmitted alleles were obtained from the meta-analysis of parent-offspring data ( n = 136,833). The maternal-only and the fetal-only effects on birth weight were extracted from a previous GWAS meta-analysis ( n = 210,248 and 297,356, respectively). The x -axis shows the SNP effect of the maternal nontransmitted alleles on gestational duration (days), and the y -axis the effect on birth weight ( z -scores). Horizontal and vertical error bars represent the standard error. The solid line depicts the inverse-variance weighted method estimate, and the dashed line the MR-Egger estimate. Colors represent the clustering of the SNP effects on gestational duration, performed using model-based clustering.
