The mean maternal age (±standard deviation) was 29.8±7.2 years.
Maternal cotinine levels were measured in maternal urine collected in the third trimester of pregnancy, using the Cotinine Micro-Plate EIA Kit (Ora Sure Technologies, Inc., Bethlehem, PA, USA).
aAdjusted for: maternal cotinine level during pregnancy, maternal alcohol consumption at conception, maternal age at pregnancy, gestational age at blood-sampling and child sex.
aAdjusted for maternal cotinine level during pregnancy, maternal alcohol consumption at conception, child sex, maternal age at pregnancy and gestational age at blood sampling.
Paternal smoking has previously been associated with fetal growth restriction and correlates with levels of maternal cotinine (22).
The associations found between maternal cotinine levels, an objective biomarker of smoking and DNA methylation in newborns imply a dose-dependent effect of maternal smoking in pregnancy (18).
We obtained similar DNA methylation differences when the metric of exposure was maternal self-report of smoking during pregnancy rather than measured maternal cotinine levels.
Higher methylation of the four MYO1G CpGs statistically significantly associated with maternal cotinine was observed with maternal smoking but did not reach epigenome-wide statistical significance.
In addition, a strong correlation between self-reported questionnaire data on smoking behaviour and plasma cotinine levels has been found (18, 40) and maternal cotinine was found to be highly correlated with the sustained smoking variable (r = 0.76) in the subsample of ARIES participants with first trimester maternal cotinine data available (N = 323).
In our study, maternal cotinine was only detectable in serum of 3 of 17 women whose partner smoked, compatible with low-level passive smoking.
