Table 1.
Participant characteristics at blood collection
| Characteristic | Cases (n = 98) |
Controls (n = 168) |
|
|---|---|---|---|
| Continuous variables | Mean ± SD | P a | |
| Age, years | 44.7 ± 4.8 | 44.6 ± 4.5 | 0.10 |
| Height, cm | 163.4 ± 6.0 | 163.5 ± 5.8 | 0.95 |
| BMI, kg/m2 | 25.7 ± 5.1 | 25.2 ± 4.8 | 0.35 |
| Menarche, years | 12.5 ± 1.3 | 12.8 ± 1.4 | 0.08 |
| Age at first pregnancy, yearsb | 22.2 ± 4.3 | 22.1 ± 4.1 | 0.92 |
| Number of term pregnancies | 2.7 ± 1.6 | 2.9 ± 1.7 | 0.50 |
| Categoric variables | Frequency, number (%) | P a | |
| Nulliparous | 9 (9.2%) | 13 (7.7%) | 0.82 |
| Smoking status | 0.50 | ||
| Never | 61 (62.2%) | 103 (61.3%) | |
| Former | 19 (19.4%) | 26 (15.5%) | |
| Current | 18 (18.4%) | 39 (23.2%) | |
| History of breast cancer in first-degree relative | 17 (17.4%) | 14 (8.3%) | 0.03 |
| Menstrual cycle day at blood collection | 0.45 | ||
| Days 0-13 | 35 (35.7%) | 68 (40.5%) | |
| Days 14-33 | 40 (40.8%) | 68 (40.5%) | |
| Days ≥34 | 9 (9.2%) | 13 (7.7%) | |
| Unknown | 14 (14.3%) | 19 (11.3%) | |
BMI, body mass index; SD, standard deviation. aP values (two-sided) were calculated by using conditional logistic regression with a Wald test. bIncludes 89 parous cases and 155 parous controls.