Despite IVF technology evolving significantly over the last 40 years, the process is far from perfect. Current research is still incredibly important to study how we can improve live birth rates, patient safety and reduce the time to live birth. 
One area of particular debate is whether a freeze all or fresh transfer approach is preferable when transferring embryos. But what is a freeze all approach and why is this discussion important?
What is a freeze all approach?
Following oocyte stimulation, retrieval and oocyte fertilisation, two options for embryo transfer are available. During a fresh embryo transfer a selected embryo can be transferred back to the mother soon after oocyte retrieval. Alternatively, the embryos can be vitrified and stored for transfer later. This is also called the “freeze all” approach, where embryos are then thawed before transfer.
The freeze all method was initially developed for the purpose of fertility preservation, such as for patients due to undergo chemotherapy. However, there is evidence that it may be a preferred option for all fertility patients. This is in light of data suggesting that staggering oocyte stimulation and embryo transfer allows the endometrium to be better primed for receipt of an oocyte. There is also evidence that it can lessen the risk of ovarian hyperstimulation syndrome (OHSS).
Effect of the freeze all method on outcomes in pregnancy, birth and neonate health
A 2014 retrospective cohort study, the largest of its kind, concluded that the use of vitrified thawed embryos did not worsen the outcomes in respect to pregnancy, birth and neonate health in comparison to the use of fresh embryos. The only notable differences were a greater number of interventions and a lower number of urinary tract infections reported with the vitrified oocyte group compared to the fresh oocyte group.
Further data from the Society for Assisted Reproductive Technology in 2011, found that gestational carriers receiving frozen-thawed embryos had 7-8% higher age-adjusted success rates than non-gestational carrier comparators receiving fresh embryos.
The programmed endometrium
There is evidence to suggest that ovarian stimulation can cause irregular endocrine milieu which could hinder embryo implantation during a fresh IVF cycle. Whereas, the freeze all method allows thawed embryos to be transferred at later cycles when the endometrium is programmed to be more receptive to freeze-thawed embryos.
Risk of OHSS
There is evidence that the risk of developing OHSS is greater during fresh IVF cycles as oocyte development, retrieval and embryo transfer occur around the same time. It has been suggested that staggering oocyte stimulation by using the freeze all method could reduce this risk. Robust randomised controlled trials are underway to determine if the freeze-all method could lessen the risk of OHSS without reducing successful treatment outcomes.
The debate continues at COGI
The World Congress on Controversies in Obstetrics, Gynecology & Infertility (COGI) congress will be held in London on 23rd-25th November, with key discussions including a debate on social freezing and a presentation titled ‘the end of freeze all?’. We will be attending to provide you with the latest updates from the conference, including research highlights and key messages.
1. Niederberger, C., Pellicer, A. and Cohen, J. et al. Forty years of IVF. Fertil Steril. 2018; 110 (2), 185-324.
2. Society for Assisted Reproductive Technology. 2010 and 2011 SART fertility success rate report. Available at: http://www.sart.org/SART_Success_Rates.
3. Cabo, A., Serra, V., Garrido, N. et al., Obstetric and perinatal outcome of babies born from vitrified oocytes. Fertil Steril. 2014; 102 (4), 1006-1015.