Adjusted* odds ratio of breast cancer for women who have had a pregnancy ending in induced abortion compared with women with no pregnancy ending in induced abortion
| Subgroup | Number of women | Odds ratio (95% CI) | p Value |
|---|---|---|---|
| *Adjusted for age, parity, and age at delivery of first child. †No information on miscarriages/induced abortions before 1981. ‡Adjusted for age only (as includes nulliparous women). §“Unknown” includes women who have had an induced abortion since 1981 (and no live births since 1981) but whose maternal history sequence before 1981 is unknown. | |||
| No abortion | 9973 | 1.00 | |
| Abortion | 2748 | 0.80 (0.72 to 0.89) | <0.001 |
| Week of gestation (of earliest abortion) | |||
| No abortion | 9973 | 1.00 | |
| <9 weeks | 203 | 0.65 (0.44 to 0.97) | 0.03 |
| 9–10 weeks | 194 | 0.93 (0.65 to 1.33) | 0.69 |
| 11–12 weeks | 63 | 0.87 (0.46 to 1.65) | 0.67 |
| >12 weeks | 119 | 0.35 (0.19 to 0.66) | <0.01 |
| Unknown | 2169 | 0.83 (0.73 to 0.93) | <0.01 |
| Age at abortion | |||
| No abortion | 9973 | 1.00 | |
| 12–19 years | 98 | 1.08 (0.64 to 1.83) | 0.76 |
| 20–24 years | 311 | 0.67 (0.48 to 0.95) | 0.02 |
| 25–29 years | 487 | 0.84 (0.66 to 1.07) | 0.15 |
| 30+ years | 1852 | 0.80 (0.70 to 0.91) | <0.01 |
| Number of abortions | |||
| 0 | 9973 | 1.00 | |
| 1 | 2383 | 0.82 (0.73 to 0.93) | <0.01 |
| 2 | 302 | 0.62 (0.45 to 0.86) | <0.01 |
| 3+ | 63 | 0.74 (0.37 to 1.48) | 0.40 |
| Time since abortion | |||
| No abortion | 9973 | 1.00 | |
| <1 year | 105 | 0.64 (0.37 to 1.09) | 0.10 |
| 1–4 years | 608 | 0.85 (0.69 to 1.05) | 0.14 |
| 5–9 years | 953 | 0.83 (0.70 to 0.99) | 0.04 |
| 10+ years | 1082 | 0.75 (0.64 to 0.89) | <0.001 |
| Temporal sequence†‡ | |||
| No abortion | 9973 | 1.00 | |
| Abortion while nulliparous | 155 | 0.77 (0.51 to 1.15) | 0.20 |
| Live birth then abortion | 876 | 0.72 (0.60 to 0.86) | <0.001 |
| Unknown sequence§ | 1717 | 0.75 (0.66 to 0.85) | <0.001 |