Fig. 1.

Estimated mean levels of mtDNA content and mtDNA methylation in placental tissue of non-smokers (n = 255), past smokers (n = 65), and current smokers (n = 62). The bars represent the estimated means with 95% confidence intervals for the non-smoking (filled circle), past-smoking (filled square), and smoking group (filled triangle). a Relative mtDNA content levels (unitless) are log₁₀-transformed; b Methylation of the MT-RNR1 gene are absolute methylation levels. Both the generalized linear model for mtDNA content and the mixed-effects model for mtDNA methylation were adjusted for maternal age, gestational age, newborn’s sex, maternal education, ethnicity, parity, pre-pregnancy BMI, and alcohol consumption. (*)p = 0.06; *p < 0.05; **p < 0.005: difference compared to the non-smoking group