Table 3.

Correlation of placental smoking index (PSI) with maternal plasma cotinine levels in VCSIP training data from smokers only ($n=72$).

Model	$r$	$p$-Value
Model 1–EPIC
Randomization	0.241	$4.14\times {10}^{-2}$
Mid-gestation	0.221	$6.24\times {10}^{-2}$
Late-gestation	0.340	$3.52\times {10}^{-3}$
Model 2–450K
Randomization	0.304	$9.42\times {10}^{-3}$
Mid-gestation	0.234	$4.82\times {10}^{-2}$
Late-gestation	0.397	$5.53\times {10}^{-4}$
Model 3–PACE
Randomization	0.276	$1.88\times {10}^{-2}$
Mid-gestation	0.231	$5.04\times {10}^{-2}$
Late-gestation	0.432	$1.49\times {10}^{-4}$

Note: PSI scores were calculated for each sample using the sum of model coefficients multiplied by normalized beta values. Maternal plasma cotinine was measured at randomization ($\text{median}=$ 18.7 wk), at mid-gestation ($\text{median}=$ 26 wk), and at late-gestation ($\text{median}=$ 31.7 wk) in the VCSIP training dataset for smokers. Maternal plasma cotinine level was either not measured or was below the limit of detection in nonsmokers and was therefore not included in the correlation analysis. $p$-Value from Pearson correlation. 450K, Illumina Methylation450K array; EPIC, Infinium MethylationEPIC array; PACE, Pregnancy And Childhood Epigenetics; VCSIP, Vitamin C to Decrease the Effects of Smoking in Pregnancy on Infant Lung Function.