Regression of endometrial thickness in combination with reduced withdrawal bleeding as a progestational effect of tibolone in postmenopausal women on oestrogen replacement therapy.

For 176 postmenopausal women on HRT with progestogen addition 'on demand' medroxyprogesterone acetate (MPA), noresthisterone and tibolone were used to protect the endometrium in 214 cases. Tibolone is a gonadomimetic steroid with combined progestogenic and estrogenic effects. In this study tibolone has been used as a progestogen. The results of these three progestogens were compared. The endometrial thickness before and after the use of progestogen was determined by vaginosonography. In 175 out of 214 cases progestogen addition during oestrogen therapy caused endometrial regression. Withdrawal bleeding was observed 166 times. If the endometrial thickness on the onset of progestogen addition was 5 mm or more, in nearly all cases withdrawal bleeding occurred when MPA or norethisterone was used. If tibolone was used, no withdrawal bleeding occurred in over half the cases studied. We report the first observation of induced endometrial regression without withdrawal bleeding.