Abstract
The freeze-all strategy has emerged as an alternative to fresh embryo transfer (ET) during in vitro fertilization (IVF) cycles. Although fresh ET is the norm during assisted reproductive therapies (ART), there are many concerns about the possible adverse effects of controlled ovarian stimulation (COS) over the endometrium. The supra-physiologic hormonal levels that occur during a conventional COS are associated with modifications in the peri-implantation endometrium, which may be related to a decrease in pregnancy rates and poorer obstetric and perinatal outcomes when comparing fresh to frozen-thawed embryo transfers. The main objective of this study was to assess the available literature regarding the freeze-all strategy in IVF cycles, in regards to effectiveness and safety. Although there are many potential advantages in performing a freeze-all cycle over a fresh ET, it seems that the freeze-all strategy is not designed for all IVF patients. There is a need to develop a non-invasive clinical tool to evaluate the endometrial receptivity during a fresh cycle, which enables the selection of patients that would benefit from this strategy. Today, it is reasonable to perform elective cryopreservation of all oocytes/embryos in cases with a risk of OHSS development, and in patients with supra-physiologic hormonal levels during the follicular phase of COS. It is not clear if all normal responders and poor responders may benefit from this strategy.
Highlights
Fresh ET is the norm during assisted reproductive therapies (ART), in the past few years, the freeze-all strategy has emerged as an alternative to fresh embryo transfer (ET) during in vitro fertilization (IVF) cycles (Roque, 2015a)
The supra-physiological hormonal levels that occur during a conventional controlled ovarian stimulation (COS) are associated with modifications in the peri-implantation endometrium, that may be related to decreases in pregnancy rates (Shapiro et al, 2011a; Roque et al, 2013), and poorer obstetric and perinatal outcomes (Maheshwari et al, 2012; Pandey et al, 2012; Pinborg et al, 2013), when comparing fresh to frozenthawed embryo transfers
There are many potential advantages in performing a freeze-all cycle over a fresh ET, it seems that the freeze-all strategy is not suited for all IVF patients
Summary
Fresh ET is the norm during assisted reproductive therapies (ART), in the past few years, the freeze-all strategy has emerged as an alternative to fresh embryo transfer (ET) during in vitro fertilization (IVF) cycles (Roque, 2015a). The technique used to evaluate the endometrium has evolved, and in 2005 Horcajadas et al published a study evaluating the endometrium gene expression profile They performed endometrial biopsies in the same oocyte donors during a fresh cycle on the 7th day after LH surge, and compared it to endometrial samples on the 7th day after hCG trigger in a stimulated cycle. When we evaluated ongoing pregnancy rates (OPR), the eFET group showed a higher OPR compared to the fresh embryo transfer group, but this difference did not reach statistical significance (RR = 1.26, 95% CI: 1.00–1.58; I2 = 0%) (Figure 1B) This new analysis included 259 in vitro fertilization (IVF) cycles in normal and high responders following blastocyst embryo transfers, considering two studies from the same reproductive center (Fig 1). These studies showed that this strategy would lead to improvements in IVF outcomes of at least 30% in CPR and OPR when compared to fresh embryo transfers
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