Table 1.
Characteristics of the study subjects and their mammographic features
| Percent density group at left exit mammogram | |||||||
| Number of women | < 20% (n = 41) | 20 to 39% (n = 43) | 40 to 59% (n = 38)a | 60 to 79% (n = 38)b | ≥ 80% (n = 5) | All women | |
| Characteristic | |||||||
| Entry screen age (years) | 164 | 40.6 (0.8) | 40.6 (0.8) | 40.7 (1.0) | 40.4 (0.8) | 41.4 (1.1) | 40.6 (0.9) |
| Exit screen age (years) | 165 | 48.6 (1.3) | 48.6 (1.5) | 48.4 (2.1) | 48.9 (1.8) | 48.5 (1.7) | 48.6 (1.7) |
| Height (m) | 164 | 1.6 (0.1) | 1.6 (0.1) | 1.6 (0.1) | 1.6 (0.1) | 1.7 (0.1) | 1.6 (0.1) |
| Weight (kg) | 163 | 77.3 (13.7) | 67.1 (11.9) | 63.0 (12.6) | 58.8 (7.6) | 54.2 (8.2) | 66.4 (13.6) |
| Body mass index (kg/m2) | 162 | 29.1 (4.9) | 25.5 (4.1) | 23.7 (4.1) | 22.0 (2.6) | 19.9 (1.8) | 25.1 (4.8) |
| Age at first birth (years) | 138 | 24.8 (5.1) | 25.3 (5.1) | 27.2 (4.9) | 27.4 (4.3) | 27.7 (7.8) | 26.1 (5.0) |
| Number of births | |||||||
| 0 | 27 (16.4) | 6 (14.6) | 4 (9.3) | 6 (15.8) | 9 (23.7) | 2 (40.0) | |
| 1 | 18 (10.9) | 4 (9.8) | 7 (16.3) | 4 (10.5) | 1 (2.6) | 2 (40.0) | |
| 2 | 79 (47.9) | 19 (46.3) | 22 (51.2) | 19 (50.0) | 18 (47.4) | 1 (10.0) | |
| 3+ | 41 (24.9) | 12 (29.3) | 10 (23.3) | 9 (23.7) | 10 (26.3) | 0 (0.0) | |
| Mammographic features | |||||||
| Entry screen, left breast | |||||||
| Total breast area (cm2) | 164 | 168.8 (70.0) | 123.6 (32.9) | 111.8 (43.7) | 100.2 (29.4) | 106.4 (48.3) | 126.3 (53.2) |
| Dense area (cm2) | 164 | 16.3 (13.0) | 38.8 (19.4) | 52.1 (22.4) | 61.7 (20.9) | 80.1 (32.2) | 42.8 (26.5) |
| Lucent area (cm2) | 164 | 152.5 (76.8) | 84.8 (33.9) | 59.6 (36.2) | 38.5 (20.7) | 26.3 (17.3) | 83.5 (63.6) |
| Percent density (%) | 164 | 13.0 (13.4) | 32.6 (15.5) | 48.0 (15.4) | 62.5 (13.3) | 76.9 (5.6) | 39.5 (23.9) |
| Exit screen, left breast | |||||||
| Total breast area (cm2) | 165 | 194.0 (76.3) | 144.6 (44.1) | 119.1 (40.6) | 105.6 (30.9) | 102.1 (37.0) | 140.7 (60.8) |
| Dense area (cm2) | 165 | 16.6 (10.3) | 42.3 (14.3) | 55.2 (17.7) | 69.8 (19.7) | 83.7 (28.9) | 46.5 (25.9) |
| Lucent area (cm2) | 165 | 177.5 (77.1) | 102.3 (34.1) | 63.9 (25.0) | 35.8 (12.6) | 18.4 (8.2) | 94.3 (69.7) |
| Percent density (%) | 165 | 9.6 (6.1) | 29.7 (5.5) | 47.0 (5.8) | 66.4 (4.4) | 82.5 (1.8) | 38.7 (22.7) |
Data presented as mean (standard deviation) or n (%). aThere were 37 women at entry and 38 women at exit; weight and body mass index are missing for one woman in this group. bHeight and weight missing for one woman (each); body mass index missing for two women in this group.