Table 1.
Age-adjusted characteristics of the study population at the time of the mammogram
| Characteristic | Premenopausal | Postmenopausal | ||
|---|---|---|---|---|
|
| ||||
| Nulliparous (n=248) | Parous (n=1600) | Nulliparous (n=198) | Parous (n=2034) | |
| Mean (SD) | ||||
| Percent mammographic density | 40.7 (19.6) | 39.2 (19.0) | 31.1 (19.9) | 25.3 (17.5) |
| Dense area (cm2) | 88.2 (51.7) | 80.6 (51.2 ) | 61.0 (44.5) | 47.9 (39.6) |
| Non-dense area (cm2) | 147.7 (94.8) | 134.8 (79.5) | 158.3 (102.6) | 156.3 (90.7) |
| Age (years)a | 44.7 (4.2) | 46.3 (4.4) | 55.3 (8.5) | 58.4 (7.7) |
| Age at menarche (years) | 12.3 (1.4) | 12.5 (1.4) | 12.3 (1.3) | 12.5 (1.4) |
| Age at menopause (years) | NA | NA | 45.9 (6.8) | 47.7 (5.9) |
| Body Mass Index (kg/m2) | 25.9 (6.5) | 25.5 (5.3) | 27.3 (6.8) | 26.2 (5.2) |
| Alcohol Use (grams) | 6.4 (9.6) | 4.3 (7.5) | 6.0 (7.7) | 5.0 (8.7) |
| Parity | NA | 2.5 (1.0) | NA | 3.1 (1.5) |
| Age at first birth (years) | NA | 26.1 (4.2) | NA | 25.1 (3.5) |
| Percentages | ||||
| Family history of breast cancer | 9 | 9 | 12 | 12 |
| Benign breast disease | 17 | 16 | 21 | 23 |
| Never used PMH | NA | NA | 30 | 35 |
| Past PMH use | NA | NA | 19 | 20 |
| Current PMH use | NA | NA | 50 | 44 |
| Breastfeeding 0–<1 month | NA | 23 | NA | 39 |
| Breastfeeding 1–6 months | NA | 16 | NA | 25 |
| Breastfeeding >6–12 months | NA | 16 | NA | 12 |
| Breastfeeding >12–18 months | NA | 13 | NA | 10 |
| Breastfeeding >18–24 months | NA | 11 | NA | 5 |
| Breastfeeding >24–36 months | NA | 12 | NA | 5 |
| Breastfeeding >36 months | NA | 9 | NA | 3 |
Abbreviations: SD= standard deviation, PMH= postmenopausal hormone, NA-not applicable
Note: Values are means (SD) and percentages and are standardized to the age distribution of the study population.
a
Value is not age adjusted