Impact on Uterine Bleeding and Endometrial Thickness: Tibolone Compared with Continuous Combined Estradiol and Norethisterone Acetate Replacement Therapy

OBJECTIVE: To evaluate endometrial thickness and the incidence of uterine bleeding in postmenopausal women using either tibolone 2.5 mg or continuous combined 2 mg estradiol and 1 mg norethisterone acetate (E+NETA) daily as hormone replacement therapy. DESIGN: We compared diary records of self-reported uterine bleeding and measurements of endometrial thickness, area, and volume by transvaginal sonography at baseline and after 1, 3, 6, and 12 months in a 1-year, prospective, randomized, double-blind, single-center trial of 100 postmenopausal women aged 46-69 years. Bleeding frequencies and endometrial thickness were assessed by Chi-square tests and analysis of covariance, respectively. RESULTS: Self-reported bleeding was significantly less in the tibolone group. Bleeding episodes were reported by 27.7% of women in the tibolone group and by 59.2% in the E+NETA group. The mean number of days with bleeding was 5.8 +/- 27.0 in the tibolone group and 35.6 +/- 58.6 in the E+NETA group. Six women in the tibolone group and seven in the E+NETA group discontinued the study; three in the E+NETA group because of bleeding. The mean endometrial thickness at baseline was 2.56 +/- 0.81 mm in the tibolone group and 2.58 +/- 1.04 mm in the E+NETA group. After 1 year, the corresponding figures were 3.32 +/- 1.58 mm and 3.07 +/- 1.68 mm. Thus, 86% of women in the tibolone group and 93% in the E+NETA group had an endometrial thickness of less than 5 mm. CONCLUSIONS: Use of tibolone 2.5 mg daily for 1 year was associated with significantly less bleeding and spotting compared with daily continuous combined 2 mg estradiol and 1 mg norethisterone acetate in postmenopausal women in the presence of both minimal and nonprogressive increase of endometrial thickness associated with the two regimens.