Table 1.

Descriptive characteristics of the study populationa

VariableCategoryN (%)
Timing of mother's smoking during pregnancybNeverQuit before pregnancyQuit during pregnancy by 18 weeksSmoked through gestational week 18520 (49.9)230 (22.1)156 (15.0)136 (13.1)
Combined grandmother's and mother's smoking during their pregnanciesc (N = 928)Neither grandmother nor mother smokedOnly grandmother smokedOnly mother smokedBoth grandmother and mother smoked607 (65.4)204 (22.0)57 (6.1)60 (6.5)
Father's smoking before the mother's pregnancy (N = 1,035)YesNo317 (30.6)718 (69.4)
Sex of the childMale556 (53.4)
Female486 (46.6)
Maternal age<25124 (11.9)
25–30504 (48.4)
>30414 (39.7)
Maternal educationLess than high school75 (7.2)
High school degree336 (32.2)
Some college464 (44.5)
4 years of college or more167 (16.0)
Parity0439 (42.1)
1425 (40.8)
2135 (13.0)
3+43 (4.1)
  • aN = 1,042 individuals in the study population. Grandmother's smoking missing for 114 and father's smoking missing for 7 individuals.

  • bDetermined by mother's self-report and mother's plasma cotinine measured during pregnancy at approximately gestational week 18, where cotinine values above 56.8 nmol/L indicate smoking.

  • c“Their pregnancies” reflects the grandmother's pregnancy with the study mother and the mother's pregnancy with the study newborn whose cord blood DNA methylation we measured.