Deferred Frozen Embryo Transfer: What Benefits can be Expected from this Strategy in Patients with and without Endometriosis?

Abstract

Progress with cryopreservation techniques have enabled development of the deferred frozen-thawed embryo transfer (DET) strategy as an alternative to relying on fresh embryo transfers. With DET, the entire embryo cohort is cryopreserved, and embryo transfer is then performed in a subsequent cycle that takes place separately from the controlled ovarian stimulation (COS). Initially developed to limit the risk of ovarian hyperstimulation syndrome that occurs with high responders, this strategy has been applied extensively with other populations in an effort to improve implantation rates. The assumption is that COS, which is essential for in vitro fertilization/intra cytoplasmic sperm injection (IVF/ICSI) procedures to obtain a multi-follicular development, could have a detrimental impact on the endometrium as a result of greatly elevated levels of steroids. It is currently not clear whether the DET strategy can be generally applied to all women requiring an IVF/ICSI procedure. The objectives of this literature review regarding DET, were hence: (i) to present the scientific background that contributed to extensive adoption of this technique, (ii) to detail the pregnancy outcomes and potential obstetric and neonatal consequences, (iii) to report on its ability to prevent risks induced by COS, and (iv) to propose indications for the DET strategy in clinical practice.