Table 2.
Hazard Ratios for rheumatoid arthritis, overall and by serologic phenotype, according to maternal smoking during pregnancy (in utero exposure) among women in the Nurses’ Health Study II (n=90,923)
| RA cases/Person-years | Base model* | +Confounders** | +Adult personal smoking and covariates (conventional)† | Controlled direct effect‡ | |
|---|---|---|---|---|---|
| All RA | |||||
| No maternal smoking | 325/1,524,879 | 1.00 (ref) | 1.00 (ref) | 1.00 (ref) | 1.00 (ref) |
| Maternal smoking | 153/578,896 | 1.23 (1.02, 1.49) | 1.25 (1.03, 1.52) | 1.14 (0.92, 1.41) | 1.10 (0.76, 1.57) |
| Don’t know/Missing | 54/236,559 | 1.03 (0.77, 1.37) | 1.04 (0.78, 1.39) | 0.98 (0.73, 1.32) | 1.01 (0.64, 1.58) |
| Seropositive RA | |||||
| No maternal smoking | 209/1,523,144 | 1.00 (ref) | 1.00 (ref) | 1.00 (ref) | 1.00 (ref) |
| Maternal smoking | 104/578,180 | 1.31 (1.03, 1.66) | 1.34 (1.06, 1.70) | 1.12 (0.86, 1.46) | 1.04 (0.67, 1.61) |
| Don’t know/Missing | 39/236,345 | 1.16 (0.82, 1.64) | 1.21 (0.86, 1.70) | 1.07 (0.75, 1.52) | 1.01 (0.58, 1.75) |
| Seronegative RA | |||||
| No maternal smoking | 116/1,521,421 | 1.00 (ref) | 1.00 (ref) | 1.00 (ref) | 1.00 (ref) |
| Maternal smoking | 49/577,267 | 1.09 (0.78, 1.53) | 1.10 (0.78, 1.53) | 1.17 (0.79, 1.72) | 1.23 (0.65, 2.32) |
| Don’t know/Missing | 15/235,895 | 0.79 (0.46, 1.35) | 0.75 (0.44, 1.30) | 0.80 (0.46, 1.39) | 1.00 (0.47, 2.14) |
Adjusted for age and questionnaire cycle.
Additionally adjusted for race/ethnicity, maternal and paternal education, maternal and paternal occupations, home ownership, state born, and family history of RA (temporally preceding confounders for the maternal smoking during pregnancy exposure).
Additionally adjusted for adult personal smoking pack-years, childhood parental smoking, adult passive smoking (years lived with a smoker since age 18), and temporally preceding covariates (birthweight, preterm birth, breastfeeding, age at menarche, body mass index at age 18, menopausal status and hormone use, parity/breastfeeding, body mass index, physical activity, alternate healthy eating index, residence, and census income).
Controlling for adult personal smoking pack-years, childhood parental smoking, adult passive smoking (years lived with a smoker since age 18) via conditioning and inverse probability weighting using temporally preceding covariates among birthweight, preterm birth, breastfeeding, age at menarche, body mass index at age 18, menopausal status and hormone use, parity/breastfeeding, body mass index, physical activity (≥ 3 metabolic equivalent), alternate healthy eating index, residence, and census income.