Long-term effects of hormone replacement therapy on the uterus and on uterine circulation

Objective: Our purpose was to study the effects of postmenopausal hormone replacement therapy on the uterus and uterine circulation. Study design: The study population consisted of 432 women, 58 to 59 years of age. Color Doppler ultrasonography with a transvaginal probe was used to measure the size of the uterus and the uterine artery pulsatility index. Results: The mean endometrial thickness in group 1 (controls without hormone replacement therapy) was significantly thinner compared with group 2 with hormone replacement therapy and with group 3 after discontinuance of hormone replacement therapy. The mean uterine artery pulsatility index was lower both in group 2 and 3 compared with group 1. When hormone replacement therapy was initiated 2 to 10 years after menopause, the endometrial thickness did not differ from that among those who had started hormone replacement therapy earlier, but the pulsatility index was significantly higher. There was positive correlation between the size of the uterus and the pulsatility index in group 1, but the correlation was negative in group 2. In general, the duration of hormone replacement therapy had no effect on the pulsatility index. Estrogen users had a significantly thicker endometrium compared with estrogen-progestogen users. The pulsatility index was highest in the estrogen users with progestogen added every month. Conclusion: The duration, onset of treatment in relation to menopause, discontinuance of hormone replacement therapy, and mode of treatment modify both the normal postmenopausal endometrial thickness and the uterine vascular resistance.