Figure 1.

DNA methylation levels of the placentas from non-smoking mothers compared with the placentas from smoking mothers. Differential methylation observed in the placentas exposed to maternal smoking is shown relative to the unexposed placentas. The model was adjusted for maternal age, BMI category, and infant gender. The placentas of mothers who quit smoking while pregnant are indicated by the red color, the placentas exposed to maternal smoking during the entire duration of the pregnancy are indicated by the blue color. On the fetal side, significant decrease in methylation was observed in the mothers that smoked throughout pregnancy at 3 CpG loci in the AHRR gene body and one CpG locus in the CYP1A1 promoter. On the maternal side of the placenta, one CpG locus in the GFI1 promoter was significantly reduced in placentas of mothers who smoked and quit (P < 0.05). None of the other genes and loci included in this study reached statistical significant differences between our exposure groups for either the maternal or the fetal side of the placenta (Supplementary Figure 1)