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How would you like your eggs, fresh or frozen?

Updated: Mar 16, 2023

To freeze, or not to freeze? That is the question

Many fertility physicians are opting to freeze all embryos, believing that transferring frozen embryos during IVF treatment results in a better pregnancy success rate than using fresh embryos. But what does the evidence say?

According to a study published in the New England Journal of Medicine in 2018, this is true in women with PCOS, who showed to have a higher live birth rate from frozen embryo transfers. Furthermore, a more recent study (2020) found no significant difference between the fresh and frozen transfer groups in terms of pregnancy rate and cumulative live birth rate (CLBRs).

Another study by Irani et al (2019) found that IVF success is heavily dependent on the quality of the embryo to be transferred, even downplaying the role of maternal age in IVF success because it has no negative impact on implantation potential or live birth success. The study obviously acknowledges the role maternal age plays in creating high quality embryos.

An interesting difference was discovered in a study of 2523 participants based on the number of oocytes retrieved. There was no statistical difference in CLBRs for women who had fewer than 10 oocytes retrieved; however, in the groups of women who had more than 11 oocytes retrieved, there was a significant difference in favour of frozen embryo transfer, as well as a significantly lower infant birth weight in the fresh embryo transfer.

Another benefit of frozen transfers is that allows for embryo testing to detect chromosomal and genetic defects, single gene disorders, and, more controversially, to select the embryo's sex before transfer. These tests help identify embryos with higher implantation potential and lower risk of miscarriage, therefore boosting IVF success rates.

Fresh embryo transfers are likely to occur five days after egg retrieval, and oestrogen levels may still be high putting implantation at risk. A frozen embryo transfer simulates a regular cycle.

In individuals who are at risk of developing ovarian hyperstimulation syndrome (OHSS), frozen transfers can help reduce the risk. Women with endometriosis and PCOS, for example, may have a better likelihood of success according to some studies.

Most of the existing data in favour of frozen embryo transfer is recent and spans no more than 15 years, and all available evidence points to a link between frozen embryo transfer and larger babies at birth and a higher risk of pre-eclampsia.


In conclusion, more high-quality research is needed, but based on present data, frozen embryo transfers are favourable when ovarian hyperstimulation is a concern. Additionally, embryo quality plays a big role in IVF success.


1. Boynukalin FK, Turgut NE, Gultomruk M, Ecemis S, Yarkiner Z, Findikli N, et al. Impact of elective frozen vs. fresh embryo transfer strategies on cumulative live birth: Do deleterious effects still exist in normal & hyper responders? PLoS One [Internet]. 2020;15(6):e0234481. Available from:

2. Stormlund S, Sopa N, Zedeler A, Bogstad J, Prætorius L, Nielsen HS, et al. Freeze-all versus fresh blastocyst transfer strategy during in vitro fertilisation in women with regular menstrual cycles: multicentre randomised controlled trial. BMJ [Internet]. 2020 [cited 2022 Mar 25];370:m2519. Available from:

3. Irani M, Zaninovic N, Rosenwaks Z, Xu K. Does maternal age at retrieval influence the implantation potential of euploid blastocysts? Am J Obstet Gynecol [Internet]. 2019;220(4):379.e1-379.e7. Available from:

4. Roque M, Valle M, Sampaio M, Geber S. Does freeze-all policy affect IVF outcome in poor ovarian responders?: Freeze-all policy in POR. Ultrasound Obstet Gynecol [Internet]. 2018;52(4):530–4. Available from:

5. Wong KM, van Wely M, Mol F, Repping S, Mastenbroek S. Fresh versus frozen embryo transfers in assisted reproduction. Cochrane Database Syst Rev [Internet]. 2017;3:CD011184. Available from:

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