Freeze-all cycle in reproductive medicine: current perspectives

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.