Table 2.
Characteristics of case and control participants.
| Variable | Control | Case | P valuea | |
| Age in years, median (IQR) | 47 (41-53) | 47 (42-54) | <.001 | |
| BMI (kg/m2), median (IQR) | 22.83 (20.96-24.77) | 22.89 (20.94-24.97) | .16 | |
| Age of menarche, median (IQR) | 14 (13-15) | 14 (13-15) | .23 | |
| Duration of reproductive lifespan, median (IQR) | 31 (27-34) | 32 (27-35) | <.001 | |
| Number of live births, median (IQR) | 1 (1-1) | 1 (1-2) | <.001 | |
| Age at first birthb, median (IQR) | 24 (22-26) | 24 (23-26) | <.001 | |
| Main residence, n (%) |
|
|
>.99 | |
|
|
Urban area | 3994 (56.04) | 3994 (56.04) |
|
|
|
Rural area | 3133 (43.96) | 3133 (43.96) |
|
| Pregnancy history, n (%) |
|
|
<.001 | |
|
|
No | 201 (2.82) | 14 (0.20) |
|
|
|
Yes | 6926 (97.18) | 7113 (99.80) |
|
| Family history of breast cancer, n (%) |
|
|
.17 | |
|
|
No | 7010 (98.36) | 6988 (98.05) |
|
|
|
Yes | 117 (1.64) | 139 (1.95) |
|
| Menopausal status, n (%) |
|
|
<.01 | |
|
|
Premenopause | 4367 (61.27) | 4547 (63.80) |
|
|
|
Postmenopause | 2760 (38.73) | 2580 (36.20) |
|
aP values are derived from Mann-Whitney U test or Pearson chi-square test.
bOnly women with at least one birth are summarized.