Preparation of the endometrium for frozen embryo transfer: an update on clinical practices

Abstract

Over the past decade, the application of frozen-thawed embryo transfer treatment cycles has increased substantially. Hormone replacement therapy and the natural cycle are two popular methods for preparing the endometrium. Hormone replacement therapy is now used at the discretion of the doctors because it is easy to coordinate the timing of embryo thawing and transfer with the schedules of the in-vitro fertilization lab, the treating doctors, and the patient. However, current results suggest that establishing a pregnancy in the absence of a corpus luteum as a result of anovulation may pose significant maternal and fetal risks. Therefore, a ‘back to nature’ approach that advocates an expanded use of natural cycle FET in ovulatory women has been suggested. Currently, there is increasing interest in how the method of endometrial preparation may influence frozen embryo transfer outcomes specifically, especially when it comes to details such as different types of ovulation monitoring and different luteal support in natural cycles, and the ideal exogenous hormone administration route as well as the endocrine monitoring in hormone replacement cycles. In addition to improving implantation rates and ensuring the safety of the fetus, addressing these points will allow for individualized endometrial preparation, also as few cycles as possible would be canceled.

Effect of different endometrial preparation protocols on pregnancy outcome of selective blastocyst transplantation

“…Compared with natural cycles, HRT cycles are more exible and convenient, making transplants easier to schedule and leading to lower cancellation rates. During the NC and mNC cycles, endometrial maturation depends on endogenous estradiol and progesterone, which are produced by growing follicles to promote endometrial proliferation and transformation [10] . Compared with the HRT cycle, the NC and mNC cycles are more physiological, less medication, and easier to operate, avoiding the possible negative effects of high dose of exogenous hormones on endometrial susceptibility [11] .…”

Comparing Day 5 versus Day 6 euploid blastocyst in frozen embryo transfer and developing a predictive model for optimizing outcomes: a retrospective cohort study

“…The natural cycle relied on endogenous hormones for optimal secretory transformation of the endometrium, while HRT utilized exogenous steroids. A few evidence based on systematic reviews and meta-analyses indicates more favorable pregnancy outcomes with natural cycles than HRT ( 39 , 40 ). This was consistent with our findings of higher live birth rates with natural cycle preparation.…”

Finding of the optimal preparation and timing of endometrium in frozen-thawed embryo transfer: a literature review of clinical evidence

“…Initially, estrogen is given to stimulate endometrial growth, followed by progesterone administration to prepare the endometrium for embryo transfer. Compared to other protocols, the AC protocol is more convenient and flexible for both patients and physicians to schedule embryo transfers with a lower cycle cancellation rate ( Table 2 ) ( 71 ). However, the disadvantages AC FET are some potential detrimental effects induced by the supplementation of exogenous estrogen and the absence of the corpus luteum.…”