Table II.
Adjusted ORs to estimate risk of type I/II invasive ovarian cancer for reproductive factors.
| Reproductive factors | Controls (N = 2100) | Type I (N = 358) |
Type II (N = 1108) |
Phet | ||
|---|---|---|---|---|---|---|
| n (%) | n (%) | ORa (95% CI) | n (%) | ORa (95% CI) | ||
| Parity | ||||||
| Nulliparous | 378 (18.0) | 160 (44.7) | 1.00 (Ref) | 287 (25.9) | 1.00 (Ref) | <0.001b |
| 1 | 267 (12.7) | 53 (14.8) | 0.44 (0.31–0.63) | 137 (12.4) | 0.64 (0.49–0.83) | |
| 2 | 667 (31.8) | 80 (22.4) | 0.27 (0.20–0.36) | 337 (30.4) | 0.63 (0.50–0.78) | |
| ≥3 | 788 (37.5) | 65 (18.2) | 0.15 (0.11–0.21) | 347 (31.3) | 0.44 (0.35–0.55) | |
| Breastfeeding (parous) | ||||||
| 0 months | 699 (40.6) | 104 (52.5) | 1.00 (Ref) | 447 (54.5) | 1.00 (Ref) | 0.006b |
| >0 to ≤4 months | 290 (16.8) | 42 (21.2) | 1.03 (0.70–1.51) | 122 (14.9) | 0.69 (0.54–0.89) | |
| >4 to ≤10 months | 242 (14.1) | 15 (7.6) | 0.43 (0.24–0.76) | 98 (11.9) | 0.65 (0.50–0.86) | |
| >10 to ≤19 months | 244 (14.2) | 13 (6.6) | 0.38 (0.21–0.69) | 93 (11.3) | 0.63 (0.48–0.83) | |
| >19 months | 247 (14.3) | 24 (12.1) | 0.79 (0.49–1.27) | 61 (7.4) | 0.47 (0.34–0.64) | |
| Ptrendc = 0.09 | Ptrendc = 0.001 | 0.85d | ||||
| Age at menarche | ||||||
| <12 years | 423 (20.1) | 72 (20.1) | 0.99 (0.71–1.38) | 246 (22.2) | 1.16 (0.94–1.45) | 0.65 |
| 12 years | 572 (27.2) | 100 (27.9) | 1.00 (Ref) | 290 (26.2) | 1.00 (Ref) | |
| >12 years | 1105 (52.6) | 186 (52.0) | 0.98 (0.75–1.28) | 572 (51.6) | 1.04 (0.87–1.25) | |
| Ptrendc = 0.67 | Ptrendc = 0.03 | 0.32d | ||||
| Menstrual cycle lengthe | ||||||
| <28 days | 245 (11.7) | 47 (13.4) | 1.00 (0.70–1.42) | 142 (12.9) | 1.06 (0.83–1.34) | 0.42b |
| 28 days | 1025 (49.1) | 196 (55.7) | 1.00 (Ref) | 561 (51.0) | 1.00 (Ref) | |
| >28 to ≤30 days | 497 (23.8) | 69 (19.6) | 0.73 (0.54–0.99) | 267 (24.3) | 0.99 (0.82–1.20) | |
| >30 days | 170 (8.2) | 19 (5.4) | 0.68 (0.41–1.13) | 66 (6.0) | 0.83 (0.61–1.13) | |
| Irregular cycles | 149 (7.1) | 21 (6.0) | 0.76 (0.47–1.24) | 65 (5.9) | 0.82 (0.60–1.13) | |
| Ptrendc = 0.05 | Ptrendc = 0.15 | 0.32d | ||||
| Age at natural menopausef | ||||||
| <45 years | 32 (2.9) | 9 (5.7) | 1.76 (0.77–4.00) | 21 (3.0) | 0.96 (0.51–1.81) | 0.02b |
| 45 to <50 years | 58 (5.2) | 11 (6.9) | 1.25 (0.60–2.61) | 49 (7.0) | 1.30 (0.80–2.13) | |
| 50 to <53 years | 991 (88.7) | 129 (81.1) | 1.00 (Ref) | 600 (85.6) | 1.00 (Ref) | |
| ≥53 years | 36 (3.2) | 10 (6.3) | 1.99 (0.91–4.36) | 31 (4.4) | 1.44 (0.81–2.56) | |
| Ptrendc = 0.67 | Ptrendc = 0.43 | 0.007d | ||||
| OC pill use | ||||||
| Never or <3 months | 766 (36.5) | 161 (45.0) | 1.00 (Ref) | 581 (52.4) | 1.00 (Ref) | 0.06b |
| 3 to <12 months | 161 (7.7) | 33 (9.2) | 1.14 (0.75–1.73) | 95 (8.6) | 0.91 (0.68–1.21) | |
| 12 to <24 months | 164 (7.8) | 25 (7.0) | 0.81 (0.51–1.28) | 92 (8.3) | 0.82 (0.62–1.10) | |
| 24 to <60 months | 378 (18.0) | 58 (16.2) | 0.85 (0.61–1.18) | 149 (13.5) | 0.60 (0.48–0.76) | |
| ≥60 months | 631 (30.1) | 81 (22.6) | 0.66 (0.49–0.89) | 191 (17.2) | 0.43 (0.35–0.53) | |
| Including non-users | Ptrendc = 0.007 | Ptrendc = <0.001 | 0.003d | |||
| IUD use | 353 (16.8) | 39 (10.9) | 0.71 (0.49–1.01) | 164 (14.8) | 1.00 (0.81–1.24) | 0.06b |
| Infertility | ||||||
| None | 1664 (79.2) | 274 (76.5) | 1.00 (Ref) | 879 (79.3) | 1.00 (Ref) | 0.53b |
| Male | 41 (2.0) | 10 (2.8) | 1.24 (0.60–2.55) | 22 (2.0) | 0.85 (0.49–1.47) | |
| Female | 161 (7.7) | 38 (10.6) | 1.35 (0.92–1.97) | 95 (8.6) | 1.05 (0.80–1.38) | |
| Cause not found | 234 (11.1) | 36 (10.1) | 0.89 (0.61–1.30) | 112 (10.1) | 0.87 (0.67–1.11) | |
| Endometriosis | 165 (7.9) | 51 (14.3) | 1.92 (1.36–2.71) | 95 (8.6) | 1.09 (0.83–1.43) | 0.003b |
| Painful periodse | 677 (32.4) | 153 (43.3) | 1.55 (1.22–1.95) | 413 (37.3) | 1.20 (1.03–1.41) | 0.04b |
| Hysterectomyg | 183 (8.7) | 23 (6.4) | 0.71 (0.45–1.13) | 111 (10.0) | 1.16 (0.89–1.51) | 0.03b |
| Tubal ligation | 419 (20.0) | 26 (7.3) | 0.40 (0.26–0.60) | 168 (15.2) | 0.91 (0.74–1.12) | <0.001b |
aModels were adjusted for age (continuous), study center (Massachusetts, New Hampshire), study phase (1992–1997, 1998–2003, 2003–2008), parity (0, 1, 2, >2), OC pill use (0, 3 months to <5 years, ≥ 5 years), family history of ovarian cancer (yes/no), family history of breast cancer (yes/no) and tubal ligation (yes/no) unless noted otherwise.
bThe P-value for heterogeneity (Phet) is from the likelihood-ratio test that compares a model with the same estimate for the association with the exposure of interest (e.g. categories of parity) across type I/II categories to a model, which allows the association of interest to vary across type I/II categories. It indicates if there were statistically significant differences in the association of interest between the different outcome categories.
cThe Ptrend is from the Wald statistic using a continuous variable.
dThe Phet is from the likelihood-ratio test that compares a model with the same estimate for the association with the exposure of interest (trend variable) across type I/II categories to a model that allows the exposure of interest to vary across type I/II categories.
eNumbers may not add up to total due to missing data.
fAnalyses were restricted to post-menopausal women and were additionally adjusted for an indicator if a participant had not had a natural menopause.
gModels were additionally adjusted for ever use of post-menopausal hormones (yes/no).