Table 3.
Rate ratios* (95% confidence intervals) and P value for linear test for trend for breast cancer incidence at postmenopausal ages (⩾50 years) by selected birth characteristics
| Birth size measure
|
No of women† (n=5173)
|
No of cases (n=296)
|
Crude analysis
|
Adjusted for gestational age
|
Adjusted for gestational age and adult risk factors‡
|
|---|---|---|---|---|---|
| Birth weight (g): | |||||
| <3000 | 954 | 60 | 1 | 1 | 1 |
| 3000-3499 | 2044 | 102 | 0.75 (0.55 to 1.03) | 0.75 (0.54 to 1.03) | 0.75 (0.54 to 1.03) |
| 3500-3999 | 1617 | 101 | 0.98 (0.71 to 1.35) | 0.98 (0.70 to 1.36) | 0.97 (0.69 to 1.35) |
| ⩾4000 | 552 | 32 | 0.89 (0.58 to 1.37) | 0.88 (0.56 to 1.37) | 0.87 (0.56 to 1.36) |
| Linear trend | P=0.83 | P=0.83 | P=0.87 | ||
| Birth length (cm):§ | |||||
| ⩽49.0 | 1442 | 77 | 1 | 1 | 1 |
| 49.5, 50.0 | 1096 | 58 | 0.97 (0.69 to 1.36) | 0.97 (0.69 to 1.37) | 0.97 (0.69 to 1.36) |
| 50.5, 51.0 | 1040 | 66 | 1.15 (0.83 to 1.60) | 1.16 (0.84 to 1.62) | 1.13 (0.81 to 1.58) |
| 51.5, 52.0 | 742 | 34 | 0.81 (0.54 to 1.21) | 0.82 (0.54 to 1.23) | 0.80 (0.53 to 1.21) |
| ⩾52.5 | 833 | 59 | 1.29 (0.92 to 1.82) | 1.30 (0.92 to 1.85) | 1.29 (0.91 to 1.84) |
| Linear trend | P=0.34 | P=0.34 | P=0.38 | ||
| Ponderal index (kg/m3): | |||||
| <24.4 | 1076 | 66 | 1 | 1 | 1 |
| 24.4-25.7 | 1010 | 55 | 0.89 (0.63 to 1.28) | 0.90 (0.63 to 1.28) | 0.88 (0.62 to 1.26) |
| 25.8-27.0 | 1089 | 65 | 1.01 (0.72 to 1.42) | 1.01 (0.72 to 1.43) | 0.99 (0.71 to 1.40) |
| 27.1-28.4 | 976 | 58 | 1.02 (0.72 to 1.46) | 1.02 (0.72 to 1.46) | 1.02 (0.71 to 1.45) |
| ⩾28.5 | 1001 | 50 | 0.85 (0.59 to 1.23) | 0.85 (0.59 to 1.23) | 0.85 (0.59 to 1.23) |
| Linear trend | P=0.68 | P=0.67 | P=0.67 | ||
| Head circumference (cm): | |||||
| <33.8 | 1335 | 80 | 1 | 1 | 1 |
| 33.8-34.0 | 967 | 42 | 0.70 (0.48 to 1.02) | 0.70 (0.49 to 1.02) | 0.69 (0.48 to 1.01) |
| 34.1-35.0 | 1501 | 77 | 0.83 (0.61 to 1.13) | 0.83 (0.60 to 1.14) | 0.82 (0.60 to 1.13) |
| 35.1-35.9 | 331 | 20 | 0.99 (0.60 to 1.62) | 0.99 (0.60 to 1.62) | 0.97 (0.59 to 1.61) |
| ⩾36.0 | 883 | 65 | 1.16 (0.84 to 1.61) | 1.16 (0.83 to 1.62) | 1.14 (0.81 to 1.60) |
| Linear trend | P=0.26 | P=0.26 | P=0.29 | ||
Estimated from Cox survival model, stratified on period of birth (1915-9, 1920-4, 1925-9) and with robust standard errors to account for correlations among siblings.
Total numbers do not always add up to 5173 because of missing data on specific birth characteristic.
Other factors as measured in 1960: marital status, children in the home (0, 1-2, 3-4, ⩾5), age at first marriage (<25, 25-29, 30-34, ⩾35 years, unmarried), level of education attained (non-academic, A levels, academic), personal car possession (yes/no), occupation (supervisor/non-manual, manual, self employed, unemployed).
Recorded to the nearest 0.5 cm.