Table 1.

Characteristics of the study sample

VariableN (%)
Age at baseline, y
    40-491,952 (52.1%)
    50-591,238 (33.0%)
    60-69559 (14.9%)
No. of pregnancies
Age at first delivery (y)*21 (5)
    0-21,597 (42.6%)
    3-41,271 (33.9%)
    ≥5881 (23.5%)
Education level
    Illiterate245 (6.7%)
    Between 1 and 7 y of education2,067 (56.6%)
    ≥8 y of education1,340 (46.7%)
Menopause after 55 y old42 (4.7%)
Menarche before 12 y old773 (19.6%)
History of HRT use445 (11.9%)
History of OC use2,789 (74.4%)
Regular breast self-examination2,087 (55.7%)
Smoking status
    Current smoker1,040 (28.3%)
    Former smoker358 (9.7%)
    No history2,275 (61.9%)
First-degree relative with history of cancer (any site)1,214 (32.4%)
First-degree relative with history of breast or ovary cancer199 (5.3%)
High genetic risk125 (3.3%)
Previous breast biopsy162 (4.3%)
BMI
    <25986 (26.3%)
    ≥25 and <301,409 (37.5%)
    ≥301,354 (36.1%)
No. of screening rounds
    1632 (16.9%)
    2887 (23.7%)
    31,134 (30.2%)
    4862 (23.0%)
    5234 (6.2%)

Abbreviations: HRT, hormone replacement therapy; OC, oral contraceptives; BMI, body mass index.

  • *Expressed as mean and SD.

  • Percentage over 1,860 women who have already entered menopause.