Prior abortion in women with breast cancer: observed numbers of women with breast cancer and prior abortion, expected numbers, the ratio of observed to expected, and 95% confidence intervals
| Interval between exposure and cancer | Observed | Expected | O/E (95% CI) | ||
| Prior abortion (all)1-150 | Breast cancer | all time intervals | 564 | 643.3 | 0.88 (0.81, 0.95)1-152 |
| 0–4 years | 97 | 110.9 | 0.88 (0.71, 1.07) | ||
| 5–9 years | 121 | 139.3 | 0.87 (0.72, 1.04) | ||
| 10–14 years | 132 | 151.8 | 0.87 (0.73, 1.03) | ||
| 15+ years | 214 | 248 | 0.86 (0.75, 0.99) | ||
| Prior induced abortion1-151 | Breast cancer | all time intervals | 300 | 362.6 | 0.83 (0.74, 0.93)1-152 |
| 0–4 years | 55 | 69.1 | 0.80 (0.60, 1.04) | ||
| 5–9 years | 70 | 82.5 | 0.85 (0.66, 1.07) | ||
| 10–14 years | 71 | 86.4 | 0.82 (0.64, 1.04) | ||
| 15+ years | 104 | 127.9 | 0.81 (0.66, 0.98) | ||
| Prior spontaneous abortion1-151 | Breast cancer | all time intervals | 41 | 44.6 | 0.92 (0.66, 1.25) |
| 0–4 years | 12 | 14.8 | 0.81 (0.42, 1.42) | ||
| 5–9 years | 11 | 12 | 0.92 (0.46, 1.64) | ||
| 10–14 years | 13 | 10.4 | 1.25 (0.67, 2.14) | ||
| 15+ years | 5 | 7.5 | 0.67 (0.22, 1.56) |
↵1-150 Includes records of abortion coded as “induced” (codes 635–6 in the International Classification of Diseases (ICD) 9th Revision) or “spontaneous” (ICD9 634) and includes records of abortion without further specification (ICD9 637); and breast cancer (ICD9 174). Equivalent codes used in ICD8 and ICD10.
↵1-151 Includes records of women with abortion coded as “induced” or “spontaneous” whether or not the woman also had records in the other categories of abortion.
↵1-152 Ratio of O/E for induced abortion to that for other abortion (that is, all minus induced): 0.88 (95% CI 0.74, 1.04).