![]() ![]() In this regard, evidence regarding the ideal FET timing (immediate versus delayed) after the freeze-all strategy mainly derives from studies, which included only artificial FET cycles ( Table 1). Ever since, a series of studies with either discrepant or difficult to explain results have followed, leaving the challenging question of the ideal timing for FET still open for debate. Hence, an increasing number of centers also started to offer the option to perform FETs in the first menstrual cycle immediately after GnRH agonist triggering. While covered by the best of intentions, the lack of clear scientific evidence to support this practice may have caused unnecessary distress to infertile patients eager to conceive as soon as possible. With this waiting period, clinicians intended to circumvent any potential hindering effect that the abrupt luteolysis following GnRH agonist triggering could have on the endometrium in a subsequent cycle. Therefore, even with the lack of evidence, it was rather common place to recommend waiting at least one menstrual cycle before the first FET after a freeze-all cycle, a habit which may have mirrored the empirical decision taken by the first researchers performing RCTs to assess the efficacy of the freeze-all strategy ( 7- 9). ![]() However, despite the ideal timing of a subsequent FET being a common concern, this had been a relatively unstudied topic until 2016. Physicians are frequently asked whether a recent ovarian stimulation attempt may pose any problem to a subsequent FET, especially following GnRH agonist triggering given the abrupt luteolysis which may perceived as harmful. To summarize, FET in a freeze-all context may have an advantage over fresh ET in good prognosis women, but not in average and certainly not in poor prognosis patients. A possible explanation for this discrepancy may be that patients with blastocyst-stage ET are favorably selected (i.e., similar to high-responders), whereas patients with cleavage-stage ET are much less favorably selected. Patients with blastocyst transfer undergoing FET were found to have improved outcomes compared to fresh ET counterparts, while those with cleavage stage transfer did not. The only difference was that in one study ET took place at the blastocyst stage ( 5) and in the other at the cleavage stage ( 6). Both studies were practically identical in design in that they tested freeze-all cycle outcomes with single ET in comparison to fresh transfer. Two recent large RCTs offered new insights into the efficacy of the freeze-all strategy. ( 4) who reported a benefit with FET solely in hyper-responders, after evaluation of 11 studies, including 5,379 patients. ![]() These findings were similar to those reported by Roque et al. In high responders, a significantly higher probability of live birth was observed in the FET group, while in normal responders no significant difference in live birth rates (LBR) between FET and fresh ET was detected. ( 3) conducted a meta-analysis that consisted of 4 RCTs (n=3,255 patients), comparing the first FET (in a freeze-all strategy) to a fresh embryo transfer (ET) in normal responders and 4 RCTs (n=2,010 patients) in high responders. Given the popularity of the freeze-all protocol and the dramatic increase of FET cycles over the last decade, several RCTs and meta-analyses aimed to evaluate the efficacy of FET versus fresh ET in different IVF populations. Freeze-all may be planned and then is referred to as “elective” freeze-all, while in some cases unplanned (or “non-elective”) freezing is performed. The freeze-all policy was first introduced by clinicians in an attempt to prevent ovarian hyperstimulation syndrome (OHSS) ( 1) and has increasingly been integrated into in vitro fertilization (IVF) for several indications, including among others progesterone rise at the end of the follicular phase, pre-implantation genetic testing for aneuploidy and embryo pooling in patients with low ovarian reserve ( 2). The practice of freezing embryos for deferred frozen embryo transfer (FET) has given rise to the so-called freeze-all strategy. Timing of frozen-thawed embryo transfer after controlled ovarian stimulation in a non-elective freeze-all policy. The article did not undergo external peer review.Ĭomment on: Huang J, Lu X, Xie Q, et al. Email: and peer review: This article was commissioned by the editorial office, Annals of Translational Medicine. Centre for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Laarbeeklaan 101 – 1090 Brussel, Belgium. Policy of Dealing with Allegations of Research MisconductĬorrespondence to: Panagiotis Drakopoulos, MD, PhD.Policy of Screening for Plagiarism Process. ![]()
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