Recent sutdies indicate that the existence of corpus lutein in the ovary is a key point to prevent preeclampsia, and patients undergoing FET with hormone replaced cycle have no corpus lutein and the absence of corpus lutein significantly increases the risk of preeclampsia in these patients. We aim to conduct a single center randomized trial study to compare the preeclampsia rate between the natural cycle and the hormone replaced cycle in patients undergoing FET.

Inclusion Criteria:

1. 18 to 42 years old women;
2. normal ovulation;
3. Scheduled to undergo frozen-thawed embryo transfer.
4. Agreeing with the informed consent.

Exclusion Criteria:

1. Those who experienced embryo transfer cycle failure for at least three times;
2. One or both of the ovaries removed;
3. Hypertention disease before embryo transfer;
4. No available embryo for transfer
5. Oocyte or sperm donated cycles