Table 1.
Baseline demographic characteristics of women with information on work schedule and time to pregnancy in the Nurses’ Health Study 3 cohort (n=1739)
| Demographic characteristics | N (%) |
|---|---|
| Age at study entry (years) | |
| <30 | 318 (18.3%) |
| 30–37 | 1017 (58.5%) |
| >37 | 404 (23.2%) |
| Body mass index (kg/m2) | |
| Underweight (<18.5) | 31 (1.8%) |
| Normal weight (18.5–24.9) | 941 (54.1%) |
| Overweight (25–29.9) | 378 (21.7%) |
| Obese (>30) | 389 (22.4%) |
| Smoking status* | |
| Never | 1349 (77.6%) |
| Former | 309 (17.8%) |
| Current | 80 (4.6%) |
| Typical hours of sleep† | |
| ≤5 | 80 (5.8) |
| 6 | 290 (20.9) |
| 7–9 | 1002 (72.3) |
| ≥10 | 14 (1.0) |
| Marital status | |
| Never married | 294 (16.9%) |
| Married | 1317 (75.9%) |
| Divorced/separated/widowed | 74 (4.3%) |
| Domestic partnership | 51 (2.9%) |
| Race | |
| White | 1583 (92.8%) |
| Black | 37 (2.2%) |
| Asian | 44 (2.6%) |
| American Indian | 2 (0.1%) |
| Hawaiian or Pacific Islander | 4 (0.2%) |
| Mixed race | 36 (2.1%) |
| Hispanic ethnicity | 72 (4.1%) |
| Pregnancy history | |
| 0 pregnancies | 1034 (59.5%) |
| 1 pregnancy | 404 (23.2%) |
| 2 pregnancies | 173 (10.0%) |
| 3+ pregnancies | 128 (7.4%) |
| Menstrual cycle regularity† | |
| Regular menses | 973 (79.3%) |
| Irregular menses | 254 (20.7%) |
| Menstrual cycle length (days)† | |
| ≤25 | 130 (10.9) |
| 26–31 | 1043 (87.2) |
| 32–50 | 20 (1.7) |
| >50 | 3 (0.3) |
Data are presented as N (%) unless otherwise noted.
*
Two women are missing information on smoking status.
†
Sleep and menstrual cycle characteristics were assessed during follow-up so not all women were eligible to have answered these questions yet.