Table 1. Baseline characteristics of the PEPI Mammographic Density Study (PEPI-MDS) participants who were randomized to estrogen+progestin therapy, and the three analytic samples used in this study.

	PEPI-MDS participants who were randomized to EPT	Analytic samples for serum progestogen analyses	Analytic samples for PGR genetic analyses	Analytic samples for serum progestogen & PGR interaction
Total N	358	280	260	210
Randomized to CEE+MPA cyclic	114	74	88	57
Randomized to CEE+MPA continuous	124	98	90	76
Randomized to CEE+MP	120	108	82	77
Non-white ethnicity, No. (%)	41 (11.5%)	35 (12.5%)	0	0
Age (mean±SD)	56.1 ± 4.3	56.2 ± 4.1	56.5 ± 4.1	56.7 ± 3.9
BMI (mean±SD)	26.2 ± 4.5	26.2 ± 4.6	26.1 ± 4.5	26 ± 4.6
Change in BMI	0.09 ± 1.3	0.04 ± 1.2	0.1 ± 1.3	0.1 ± 1.3
Baseline progesterone level (pg/ml; mean±SD)	202.2 ± 259.6	172.9 ± 44.4	208.6 ± 287.4	173.1 ± 45.2
Baseline mammographic density (%; mean±SD)	24.1 ± 18.2	24.0 ± 18.2	24.5 ± 18.5	24.4 ± 18.5
Parous women, No. (%)	321 (89.7%)	253 (90.4%)	236 (90.8%)	191 (91.0%)
Smoking status, No. (%)
Current	39 (10.9%)	29 (10.4%)	31 (11.9%)	23 (11.0%)
Former	130 (36.3%)	101 (36.1%)	101 (38.9%)	80 (38.1%)
Never	189 (52.8%)	150 (53.6%)	128 (49.2%)	107 (51.0%)
Alcohol use, No. (%)
> 5.43 (g/day)	110 (30.7%)	82 (29.3%)	83 (31.9%)	64 (30.5%)
> 0, = 5.43 (g/day)	122 (34.1%)	99 (35.4%)	95 (36.5%)	78 (37.1%)
None	126 (35.2%)	99 (35.4%)	82 (31.5%)	68 (32.4%)
Level of physical activity, No. (%)
High	116 (32.4%)	91 (32.5%)	86 (33.1%)	68 (32.4%)
Medium	123 (34.4%)	103 (36.8%)	92 (35.4%)	81 (38.6%)
Low	119 (33.2%)	86 (30.7%)	82 (31.5%)	61 (29.1%)
Hysterectomy, No. (%)	106 (29.6%)	82 (29.3%)	79 (30.4%)	65 (31.0%)
Prior use of hormone therapy, No. (%)	203 (56.7%)	157 (56.1%)	158 (60.8%)	127 (60.5%)
Adherence to treatment assignment, No. (%)	323 (90.2%)	265 (94.6%)	242 (93.1%)	204 (97.1%)

Abbreviations: CEE, conjugated equine estrogens; MPA, medroxyprogesterone acetate; MP, micronized progesterone