Table 3. Association between a history of GDM and incident invasive breast cancer risk, stratified by risk factors.
| Stratified by Risk Factors | Cases– No. No GDM / GDM | No GDM HR (95% CI) | GDM HR (95% CI) | P for interaction |
|---|---|---|---|---|
| Current BMI category (kg/m2)* | ||||
| Normal (<25.0) | 1116 / 49 | 1.00 (reference) | 0.97 (0.72-1.32) | 0.04 |
| Overweight (25.0-29.9) | 646 / 25 | 1.00 (reference) | 0.50 (0.32-0.78) | |
| Obese (≥30.0) | 512 / 26 | 1.00 (reference) | 0.50 (0.32-0.77) | |
| Age at first birth | ||||
| <30 years | 1707 / 59 | 1.00 (reference) | 0.57 (0.39-0.83) | 0.85 |
| ≥30 years | 570 / 41 | 1.00 (reference) | 0.89 (0.64-1.24) | |
| Family history of breast cancer | ||||
| No | 1900 / 83 | 1.00 (reference) | 0.65 (0.52-0.83) | 0.96 |
| Yes | 377 / 17 | 1.00 (reference) | 0.76 (0.44-1.31) | |
| Family history of diabetes | ||||
| No | 1669/62 | 1.00 (reference) | 0.75 (0.57-0.98) | 0.33 |
| Yes | 608/38 | 1.00 (reference) | 0.59 (0.41-0.85) | |
| Physical Activity | ||||
| Low (Q1-Q3) | 1457 / 58 | 1.00 (reference) | 0.56 (0.42-0.74) | 0.04 |
| High (Q4-Q5) | 820 / 42 | 1.00 (reference) | 0.98 (0.70-1.37) | |
| Total lifetime breastfeeding | ||||
| None to <6 months | 933 / 29 | 1.00 (reference) | 0.55 (0.37-0.81) | 0.08 |
| ≥6 months | 1344 / 71 | 1.00 (reference) | 0.77 (0.59-0.99) |
HR=hazard ratio, CI=confidence interval
Multivariable model adjusts for age, body mass index at age 18 (continuous), weight gain since age 18 (continuous), height (continuous), total physical activity (MET-hours/week, quintiles), alcohol intake (none, 1-14 grams/day, ≥15 grams/day), age at menarche (≤10 years old, 11-12, 13-14, ≥15), birth index (continuous), total breastfeeding (none, <6 months, ≥6 months), menopausal status (premenopausal, postmenopausal, unknown), hormone therapy use (never, ever use of estrogen + progesterone, past – estrogen only or other, current – estrogen only or other), family history of breast cancer in mother or sister (yes/no), personal history of benign breast disease (yes/no), White race/ethnicity (yes/no), and mammography within the past 2 years (<40 years old, ≥40 and no mammography, ≥40 and mammography for screening, ≥40 and mammography for abnormality/symptoms).
Multivariable model is adjusted for current BMI (continuous).