TABLE 4.
Incidence rate ratios for uterine leiomyomata according to estrogenic potency, progestational potency, progestin classification, and formulation of oral contraceptives, Black Women’s Health Study, 1997–2001
| Hormonal contraceptive use | Person-years (no.) | All cases
|
|||
|---|---|---|---|---|---|
| Cases (no.) | Age-adjusted IRR*,† | Multivariate IRR‡ | 95% CI* | ||
| Never users§ | 13,918 | 386 | 1.0 | 1.0 | Referent |
| Estrogenic potency¶ | |||||
| Low (<30 μg) | 6,278 | 175 | 1.1 | 1.1 | 0.9, 1.3 |
| Medium (30–39 μg) | 4,663 | 119 | 1.1 | 1.0 | 0.8, 1.3 |
| High (≥40 μg) | 3,767 | 108 | 1.2 | 1.2 | 0.9, 1.5 |
| ptrend | 0.90 | ||||
| Progestational potency# | |||||
| Low (<1 mg) | 10,489 | 272 | 1.1 | 1.1 | 0.9, 1.2 |
| Medium (1 mg) | 1,432 | 46 | 1.2 | 1.2 | 0.9, 1.6 |
| High (>1 mg) | 2,787 | 84 | 1.2 | 1.2 | 0.9, 1.5 |
| ptrend | 0.31 | ||||
| Classification of progestin** | |||||
| Gonane | 7,798 | 195 | 1.0 | 1.0 | 0.9, 1.2 |
| Levonorgestrel, norgestrel | 4,519 | 119 | 1.0 | 1.1 | 0.9, 1.3 |
| Desogestrel | 1,157 | 30 | 1.1 | 1.1 | 0.7, 1.5 |
| Norgestimate | 2,122 | 46 | 0.9 | 0.9 | 0.7, 1.2 |
| Estrane | 8,301 | 250 | 1.1 | 1.2 | 0.9, 1.4 |
| Norethindrone, norethindrone acetate | 7,734 | 226 | 1.1 | 1.1 | 0.9, 1.3 |
| Ethynodiol diacetate | 567 | 24 | 1.7 | 1.6 | 1.1, 2.5 |
| Estrogen formulation# | |||||
| Monophasic | 9,398 | 276 | 1.1 | 1.1 | 0.9, 1.3 |
| Biphasic or triphasic | 6,524 | 165 | 1.1 | 1.1 | 0.9, 1.3 |
IRR, incidence rate ratios; CI, confidence interval.
Adjusts for age (1-year intervals) and time period (1997–1999, 1999–2001).
Adjusts for age, time period, age at menarche, parity, age at first birth, years since last birth, body mass index, smoking, alcohol, and education.
Reference category for all comparisons. All analyses exclude current users of progestin-only injectables and implants (29 cases; 2,167 person-years).
In ethinyl estradiol equivalents per day. Estrogenic activity of entire tablet, as measured by mouse uterine assay (27). Omits 106 cases and 5,338 person-years with missing information on oral contraceptive dose.
In norethindrone equivalents per day: 1 mg of norethindrone = 1 mg of norethindrone acetate = 1 mg of ethynodiol diacetate = 0.2 mg of norgestrel = 0.1 mg of levonorgestrel (27). Omits 106 cases and 5,338 person-years with missing information on oral contraceptive dose.
Omits 34 cases and 1,780 person-years with missing information on oral contraceptive brand.