Natural Cycle Versus Hormone Replaced Cycle in Frozen-thawed Embryo Transfer: a Randomized Controlled Non-inferiority Trial

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 controlled non-inferiority trial to compare the live birth rate and gestational hypertention disease rate between the natural cycle and the hormone replaced cycle in women undergoing FET.

The investigators plan to enroll women scheduled for frozen-thawed cycles. Eligible participants will be randomised 1:1 to the natural cycle and the hormone replaced cycle for endometrium preparation. All other IVF procedures will be carried out following a routine method in each center. Women will be followed up until six months after randomisation for those who fail to get pregnant after the completion of the first embryo transfer or delivery for those who get pregnant after the embryo transfer. The primary outcome is live birth after the embryo transfer. Primary analysis will be by intention-to-treat analysis. A 10% live birth is considered to be valid. Considering 10% loss to follow-up with a significance level at 0.05 and a power of 80%, the investigators plan to recruit 960 women to demonstrate women treated with natural cycle have no inferiority regarding live birth rate than those treated with hormone replacement cycle.