Abstract: Objective：To investigate the levels of sera estrogen and progesterone, and the expression level of endometrial telomerase, in those recurrent spontaneous abortion（RSA） patients in the window of implantation (WOI), so as to explore the pathophysiology of RSA. Methods：The endometrial samples were collected from 32 cases of RSA and 25 cases of normal pregnant women with the informed consent. The levels of sera estrogen and progesterone were tested by chemiluminescence. The endometrial morphology was checked by hysteroscopy. The expression level of endometrial telomerase the time of WOI was tested by immunohistochemistry and real-time PCR. Results：①56.3% patients of RAS had the so-called "bad type" endometrium under hysteroscopy, and 40.6% RSA patients had unsynchronous response in endometrial glands and stroma. In the control group, 84% women had the so-called "good type" endometrium, and 88% had synchronous response. ②There was a linear correlation between the telomerase activity in the WOI and the E2/P ratio（r=0.947 5）. The telomerase activity in the RSA group was significantly higher than that in the control group （P＜0.05）. ③The expression of telomerase was found in both the epithelial cells and the stromal cells in the WOI endometrium. There was no significant difference in the telomerase expression in the epithelial cells between two groups（P＞0.05）, while the expression in the stromal cells of the RSA group was significantly increased when compared with the control group（P＜0.05）. Conclusions：①The endometrial morphology in the WOI under hysteroscopy is helpful to understand the endometrial receptivity of RSA patients. ②The disorder of endometrial telomerase activity in the WOI may be related to RSA. ③The levels of serum estrogen and progesterone combined with the endometrial telomerase activity were used to evaluate the endometrial receptivity, which is benefit to improve the treatment of RSA.

Key words: Recurrent spontaneous abortion, Endometrium, Progesterone, Telomerase, Window of implantation