Figure 4.

Mediation analysis showing that part of the effect of periconceptional smoking on fetal growth parameters and birth weight can be explained by a delayed embryonic morphology. The asterisk (*) below the bar indicates significant effect. Note that the mediated proportion for head circumference in Model 1 could not actually be interpreted due to opposite direct and indirect effect estimates. 1^a Crude model. 2^b Model adjusted for alcohol use, educational level, folic acid supplement use, maternal age, mode of conception, ethnicity, fetal sex, maternal BMI, parity and vitamin use. AC, abdominal circumference; BW, birth weight; FL, femur length; HC, head circumference. Growth parameters are expressed as Z-scores, which are corrected for gestational age. Birth weight is expressed as Z-score, which is corrected for sex and gestational age. The total effect of smoking on fetal growth parameters and birth weight is reported by effect estimates (β) with 95% CIs and is decomposed into a direct effect and an indirect effect mediated by Carnegie developmental stages.