Low dose continuous combined hormone replacement therapy: early and late postmenopausal effect on endometrium

We investigated endometrial response to low (25 microg through the skin estradiol plus 700 microg norethindrone) and standard dose (2 mg oral estradiol plus 1 mg norethindrone acetate or 700 microg norethindrone) continuous combined therapy in postmenopausal women with time and bone mineral density response. Endometrial thickness was distributed logarithmically, with the means after use of 25 microg estradiol (4.3 mm) and 2 mg estradiol (3.8 mm) being similar. Subjects studied 15.4 +/- 7.0 months apart showed a difference of endometrial thickness of -0.55 +/- 1.3 mm. Neither pretreatment bone mineral density nor change correlated with endometrial thickness. Age, estrogen dose, bone mineral density, weight, and time on treatment do not relate to endometrial thickness. A commonly regarded cutoff point for biopsy, an endometrial thickness of 8 mm, is about 1 SD greater than the mean.