Fig. 2

The mediation effects. Girls (a) and boys (b). θ1 is the estimated effect (ln OR) of CpG 11 methylation on FT-LBW adjusting for confounders. θ1’ is the estimated effect (ln OR) of CpG 11 methylation on FT-LBW additionally introducing placental surface area into model. θ2 is the estimated effect (ln OR) of placental surface area on FT-LBW adjusting for confounders. β1 is the coefficient of CpG 11 methylation on placental surface area. Confounders include maternal age, education, family monthly income, ETS exposure during pregnancy, and gestational age. *P value < 0.05; **P value < 0.01