Placental mitochondrial DNA and CYP1A1 gene methylation as molecular signatures for tobacco smoke exposure in pregnant women and the relevance for birth weight

Table 2 Effect of tobacco smoking status during pregnancy on CpG sites of CYP1A1 in placental tissue (n = 382)

CYP1A1 methylation^a	Non-smoking	Past-smoking			Smoking
CYP1A1 methylation^a	Non-smoking	%	(95% CI)	p value	%	(95% CI)	p value
CpG 1	Ref.	−1.16	(−5.90 to 3.56)	0.99	1.75	(−3.09 to 6.60)	0.95
CpG 2	Ref.	−0.30	(−4.25 to 3.66)	0.99	0.43	(−3.63 to 4.49)	0.99
CpG 3	Ref.	0.02	(−2.47 to 2.51)	0.99	−4.57	(−7.15 to −1.98)	<0.0001
CpG 4	Ref.	1.00	(−2.11 to 4.11)	0.98	0.98	(−2.22 to 4.19)	0.99

Data shown in italic is significant
Mixed-effects models are adjusted for maternal age, gestational age, newborn’s sex, maternal education, ethnicity, parity, pre-pregnancy BMI, and alcohol consumption
^aEstimated absolute percentage (%) change in methylation levels for each CpG of CYP1A1 compared to the non-smoking group (reference). The 95% CI and p values are adjusted according to Dunnett’s procedure

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