Freeze-all strategy in IVF/ICSI cycles: an update on clinical utility.

Over the years concerns have arisen about possible adverse effects associated with controlled ovarian stimulation (COS) as regards not only the endometrium, but also on obstetrical and perinatal outcomes in pregnancies after fresh embryo transfer (ET) during in-vitro fertilization (IVF) treatment. The improvements in cryopreservation techniques associated with the possible impairment in endometrial receptivity due to the supra-physiologic hormonal levels observed during conventional COS have increased the implementation of the so-called "freeze-all" policy. With this strategy, the entire cohort of embryos is cryopreserved to be transferred to the uterus in subsequent cycles in a more physiological environment, avoiding the supra-physiologic hormonal levels observed during COS. The initial studies showed that this strategy could be beneficial for subgroups of patients, however, the freeze-all policy is being more and more frequently used for all patient categories. Unfortunately, currently, no clinical data support this widespread use of the freeze-all strategy. Based on available trials, it seems justified to implement the strategy in patients with risk of ovarian hyperstimulation syndrome, hyper-responders and when performing preimplantation genetic testing for aneuploidy in blastocyst stage. Therefore, all the other indications, such as implantation failure, high progesterone levels on the trigger day, advanced maternal age, and endometriosis, still lack the evidence to support routine use of the freeze-all policy.