Prospective clinical study ：observing the correlation between endometrial elasticity score, endometrial blood flow index (PI, RI, S/D, endometrial thickness, morphology) and clinical pregnancy rate. In order to find a non-invasive, convenient and comprehensive evaluation method of evaluating the endometrial receptivity, and to provide effective means for the frozen embryo transplantation patients to improving pregnancy outcome.

Randomly selecting 20-40 years patients were prepared to accept frozen embryo transplant ; HRT cycle preparation of endometrium；choosing HRT plan to prepare the transplantation endometrium.Establishing a strict standard of exclusion and exclude standard to exclude endometrial lesions and underlying disease.The patients were given elastography for 5-7 days afterEndometrium transformation.Observing the correlation between endometrial elasticity score, endometrial blood flow index (PI, RI, S/D, endometrial thickness, morphology) and clinical pregnancy rate. In order to find a non-invasive, convenient and comprehensive evaluation method of evaluating the endometrial receptivity, and to provide effective means for the frozen embryo transplantation patients to improving pregnancy outcome.

Inclusion Criteria:

1. the volunteers voluntarily signed the informed consent.
2. female patients between 20-40 years old.
3. HRT cycle.
4. no uterine cavity operation was performed within 3 months.

Exclusion Criteria:

1. endometrial polyps, abnormal uterine cavity, intrauterine adhesions and dysplasia of uterus.
2. hydrosalpinx was not ligated.
3. patients with uterine myoma and uterine fibroids;

In order to find a non-invasive, convenient and comprehensive evaluation method of evaluating the endometrial receptivity, and to provide effective means for the frozen embryo transplantation patients to improving pregnancy outcome.