The effects of oral estriol on the endometrium in postmenopausal women.

OBJECTIVES To study the long-term effects of oral estriol tablets on the endometrium of postmenopausal women by TVS and histology. METHOD This was a cross sectional, parallel-group, multicenter trial of 241 postmenopausal women, out of whom 125 were treated with oral estriol and 116 were untreated controls. Endometrial histology using Pipelle biopsies and/or dilatation and curettage (D&C) was taken, endometrial thickness was assessed by use of transvaginal ultrasound (TVS), and the relation between endometrial thickness and histology was calculated. RESULTS No statistically significant differences between the two groups were found in endometrial histology. There were found more polyps in the oral estriol group (14.0%) as compared with the control group (2.9%). The mean endometrial thickness in the oral estriol group was 3.0 mm compared with a mean value of 2.4 mm in the control group: P=0.01. CONCLUSIONS No clinically relevant difference was found between the endometrium status (assessed by histology and TVS) of postmenopausal women on long-term oral estriol therapy and untreated controls. This trial supports the endometrial safety of maintenance treatment with oral estriol tablets. However, there are signs, not statistically significant, that may be associated with more endometrial polyps in postmenopausal women than if therapy is not given and that TVS is a useful instrument for the diagnosis.