Comparison of endometrial growth produced by unopposed conjugated estrogens or by micronized estradiol in postmenopausal women.

Abstract

When unopposed estrogen replacement treatment is used, what is the pattern of endometrial growth? Does endometrial growth differ for various dosages and formulations? A total of 87 postmenopausal women, median age 57 years (mean 56.7 +/- 5.6 years, range 45 to 69 years), were studied in a prospective, randomized, open clinical trial lasting 24 weeks. The treatment arms consisted of micronized estradiol, 0.5 or 1.0 mg (Estrace, Bristol-Myers Squibb, Princeton, N.J.), and conjugated estrogens, 0.625 mg (Premarin, Wyeth-Ayerst, Philadelphia). Endometrial thickness was evaluated by vaginal probe ultrasonography at outset and after 6, 12, and 24 weeks of treatment. Endometrial growth was progressive over time; more than half the total 24-week growth occurred in the first 6 weeks. The mean weekly rate (+/-SD) of endometrial growth was similar for micronized estradiol, 1.0 mg, and conjugated estrogens, 0.625 mg (0.19 +/- 0.15 mm for micronized estradiol, 1.0 mg, and 0.19 +/- 0.14 mm for conjugated estrogens, 0.625 mg). These rates differed to a statistically significant degree (p < 0.05) from the growth rate produced by micronized estradiol, 0.5 mg (0.08 +/- 0.16 mm). Both unscheduled and scheduled uterine bleeding was less likely among women using micronized estradiol, 0.5 mg, than among women using micronized estradiol, 1.0 mg, or conjugated estrogens, 0.625 mg. In a 24-week trial the therapeutically equivalent estrogen doses produced the same mean increment in endometrial thickness, but half-strength estradiol produced half as much endometrial growth.