The impact of HRT on endometrial thickness—do cut‐off values exist?

Purpose To assess the reference standards for endometrial thickness in patients in Hormonal Replacement Therapy according to the different regimens of therapy. Methods Eight centres participated in this study. Main criteria for inclusion in this study were a) at least nine months from menopause and b) at least six months of HRT. Bi-endometrial thickness was measured by transvaginal ultrasound (tvs) in patients on sequential or combined HRT regimens. Women following sequential regimen underwent TVS examination immediately after the withdrawal bleeding, always between 5 and 10 days from the last progesterone tablet. Hysteroscopy and biopsy were performed within 5 days from TVS in all patients with an endometrial thickness > 4.5 mm. Results 589 patients met the entry criteria. Mean years of HRT treatment were 3.2 ± 2.2. In patients undergoing sequential HRT and combined HRT the mean (± sd) endometrial thickness were 3.5 ± 1.2 mm and 3.6 ± 2 mm. An endometrium > 4.5 mm was observed in 121 patients (20.5%). Hyperplasia, polyps and endocavitary fibroids were found in 15%, 24% and 8% of cases respectively. The positive predictive value of TVS examination was 47%. Endometrial thickness was the only variable significantly and independently associated to histologic abnormalities and endocavitary fibroids. Conclusions Sonographic endometrial thickness of 4.5 mm, provides a sensitive tool to select HRT patients who might benefit from hysteroscopy and biopsy.