Table 1.
Descriptive Characteristics of Study Sample (n = 700), Early Determinants of Mammographic Density Study, United States, 1959–2008
| Characteristic | Overall | Sibling Subset | ||||
|---|---|---|---|---|---|---|
| No. | % | Mean (SD) | No. | % | Mean (SD) | |
| Maternal variables | ||||||
| Maternal age at registration, years | 700 | 26.2 (5.9) | 254 | 25.8 (5.5) | ||
| Paternal age at registration, years | 672 | 29.4 (6.8) | 248 | 29.1 (6.8) | ||
| Maternal prepregnancy BMIa | 656 | 23.3 (3.8) | 248 | 23.2 (4.0) | ||
| Maternal gestational weight gain, kg | 675 | 9.2 (4.0) | 249 | 8.7 (4.0) | ||
| Maternal education at registration | ||||||
| Less than high school | 180 | 25.9 | 56 | 22.0 | ||
| High-school graduate | 289 | 41.6 | 112 | 44.1 | ||
| Some college, technical/trade school, or college graduate | 225 | 32.4 | 86 | 33.9 | ||
| Prenatal smoking exposureb | ||||||
| Yes | 272 | 40.1 | 112 | 45.2 | ||
| No | 406 | 59.9 | 136 | 54.8 | ||
| Birth variables | ||||||
| Birth weight, kg | 700 | 3.4 (0.5) | 254 | 3.3 (0.5) | ||
| Birth length, cm | 696 | 51.2 (3.0) | 252 | 50.7 (3.0) | ||
| Early growth variables | ||||||
| Weight at 4 months, kg | 700 | 6.4 (0.8) | 254 | 6.2 (0.8) | ||
| Length at 4 months, cm | 696 | 62.4 (2.9) | 250 | 61.8 (3.2) | ||
| Weight at 1 year, kg | 693 | 9.7 (1.3) | 252 | 9.4 (1.3) | ||
| Length at 1 year, cm | 689 | 73.9 (3.2) | 248 | 73.4 (3.2) | ||
| Weight at 4 year, kg | 661 | 16.8 (2.4) | 237 | 16.3 (2.2) | ||
| Length at 4 year, cm | 656 | 100.7 (4.9) | 234 | 100.2 (4.9) | ||
| Adult variables | ||||||
| Race/ethnicityb | ||||||
| Non-Hispanic white | 546 | 78.2 | 201 | 79.5 | ||
| Non-Hispanic black | 86 | 12.3 | 27 | 10.7 | ||
| Hispanic | 40 | 5.7 | 14 | 5.5 | ||
| Non-Hispanic API and other | 26 | 3.7 | 11 | 4.3 | ||
| Weight, kg | 686 | 75.2 (18.6) | 248 | 75.6 (19.0) | ||
| Height, m | 698 | 1.7 (0.1) | 252 | 1.7 (0.1) | ||
| BMIa | 686 | 27.5 (6.4) | 248 | 27.7 (6.8) | ||
| Age at interview, years | 700 | 44.1 (1.8) | 254 | 44.0 (1.8) | ||
| Age at mammogram, years | 700 | 43.1 (2.3) | 254 | 43.1 (2.2) | ||
| % density | 700 | 31.8 (18.7) | 254 | 30.3 (19.2) | ||
| Dense area, cm2 | 700 | 35.8 (22.0) | 254 | 33.6 (22.2) | ||
| Breast area, cm2 | 700 | 137.8 (74.0) | 254 | 138.4 (73.0) | ||
Abbreviations: API, Asians and Pacific Islanders; BMI, body mass index; SD, standard deviation.
a Weight (kg)/height (m)2.
b Values do not sum to total due to missing data.