Table 1.
Descriptive characteristics of the study populationa
| Variable | Category | N (%) |
|---|---|---|
| Timing of mother’s smoking during pregnancy b | Never | 520 (49.9) |
| Quit before pregnancy | 230 (22.1) | |
| Quit during pregnancy by 18 weeks | 156 (15.0) | |
| Smoked through gestational week 18 | 136 (13.1) | |
| Combined grandmother’s and mother’s smoking during their pregnancies c (N=928) | Neither grandmother nor mother smoked | 607 (65.4) |
| Only grandmother smoked | 204 (22.0) | |
| Only mother smoked | 57 (6.1) | |
| Both grandmother and mother smoked | 60 (6.5) | |
| Father’s smoking prior to the mother’s pregnancy (N=1,035) | Yes | 317 (30.6) |
| No | 718 (69.4) | |
| Sex of the child | Male | 556 (53.4) |
| Female | 486 (46.6) | |
| Maternal age | <25 | 124 (11.9) |
| 25–30 | 504 (48.4) | |
| >30 | 414 (39.7) | |
| Maternal education | Less than high school | 75 (7.2) |
| High school degree | 336 (32.2) | |
| Some college | 464 (44.5) | |
| 4 years of college or more | 167 (16.0) | |
| Parity | 0 | 439 (42.1) |
| 1 | 425 (40.8) | |
| 2 | 135 (13.0) | |
| 3+ | 43 (4.1) |
a
N=1,042 individuals in the study population. Grandmother’s smoking missing for 114 and father’s smoking missing for 7 individuals.
b
Determined 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.