Each step of IVF treatment comes with new, important choices that must be made. One key decision is whether to choose a fresh or frozen embryo transfer.
Whether you choose a fresh or frozen embryo transfer, the initial steps of your IVF treatment will look quite similar.
In a “stimulated” IVF cycle, you will take medication that stimulates your ovaries to grow many mature egg follicles. Your cycle is monitored to watch the growth of the uterine lining (endometrium) and follicles.
When enough follicles are an appropriate size, your eggs will be retrieved in the clinic. For patients choosing a fresh embryo transfer, the uterine lining will also be evaluated to ensure it is thick enough to support the embryo after transfer.
The retrieved eggs are fertilized using sperm from your partner or donor and the resulting embryos develop for 5-7 days, with embryologists monitoring their growth and relaying information on their development back to you.
Now, you can either choose to:
- 1. Freeze the well-developed embryos in the lab for future use
- 2. Immediately undergo a fresh embryo transfer
Is one method more successful?
In 2016, the Canadian Fertility and Andrology Society reported on the success rates of fresh vs frozen embryo transfers in clinics across Ontario and Quebec. For each transfer method, the chances of achieving one live birth per round of IVF are reported in the table below.
| Fresh Embryo Transfer | Frozen Embryo Transfer | |
| Women under 35 | 41% | 31% |
| Women 35-39 | 30% | 24% |
| Women 40+ | 14% | 15% |
When looking at the above success rates, it seems that choosing a fresh-embryo transfer would be a no-brainer for individuals under 40 years of age. However, as expected, the decision is more complicated than this. Studies have shown that there are many reasons why a frozen embryo transfer (FET) might be more beneficial than a fresh transfer.
Ovarian Hyperstimulation Syndrome (OHSS)
Specifically, FET might be recommended for women at risk of developing ovarian hyperstimulation syndrome (OHSS), a complication of stimulated IVF cycles. Cases of OHSS fall into one of two categories: early-onset or late-onset.
- Early-onset OHSS can sometimes result from the medication used to stimulate the ovaries before an egg retrieval. While FET cannot prevent early-onset OHSS, it allows for time to manage the condition without impacting the pregnancy1.
- Late-onset OHSS occurs after implantation and pregnancy and is caused by hCG release from the placenta. This type of OHSS is more likely to cause serious symptoms but can be almost entirely prevented through FET1.
Polycystic ovary syndrome (PCOS) is a condition known to increase the risk of developing OHSS, so individuals with this condition may benefit from transferring frozen embryos. A 2018 study from the New England Journal of Medicine found that for PCOS patients, FET was associated with a higher rate of live births and a lower risk of OHSS2.
The window of receptivity
Before egg retrieval, medication stimulates the ovaries to release as many mature eggs as possible. This process affects the timing of the “window of implantation,” which refers to the menstrual cycle days where the endometrium is ready to receive a fertilized embryo. This window usually falls about 8-10 days after ovulation. However, when the ovaries have been stimulated to produce many eggs, progesterone and estrogen levels can increase ten times higher than usual. The endometrium rushes to prepare itself to receive an embryo in response to these high levels. Studies have shown that this shifts the window of implantation, with it arriving sooner than normal3.
It is important to remember that even after egg retrieval and fertilization, the embryos must still develop for around five days before they will be ready for transfer. With a window of implantation shifted sooner than expected, the endometrium might not be receptive anymore, and the chance of implanting could be lower. Conversely, a frozen cycle allows the individual’s hormones to rebalance before transferring an embryo. This means that the window of implantation can return to its expected timing before transfer.
Are there any other factors to consider?
When making your decision on whether to pursue a fresh or frozen embryo transfer, you should first ask yourself some essential questions:
Does my clinic offer both options for transfer?
Many clinics universally recommend freezing embryos. This rest period allows the body to recover from stress associated with the procedure and pre-IVF medication to increase the chance of successful implantation. For this reason, not every clinic offers the option of fresh embryo transfer. If you are deciding between the two methods, you should first ask your clinic if both options are available.
Do I want to perform genetic testing on my embryos?
Embryos will typically need to be frozen if you elect to have genetic testing performed on them. Pre-implantation genetic testing (PGT), such as PGT-A or PGT-M, is a valuable screening tool to identify abnormal chromosome numbers or the embryo’s likelihood of developing a genetic disease.
What are my progesterone levels before egg retrieval?
As previously mentioned, high estradiol and progesterone levels before egg retrieval can shift the window of implantation. If you have an abnormally high progesterone level before your egg retrieval, your doctor may suggest a frozen embryo transfer to allow your body and hormonal balance to recover.
What will my embryo transfer process look like at Anova?
Anova Fertility offers both fresh and frozen embryo transfers. We encourage our patients to discuss both options with their physician, as one may be better suited to their fertility goals. Although there is a small chance of an embryo not surviving the thawing process, frozen embryo transfers have the added benefit of allowing the patient’s body to recover and the option to proceed with PGT-A and/or PGT-M testing. While both types of transfers are offered, it is highly dependent on the personalized plan created for you by your physician, with your best interest in mind.
Are you looking into IVF and have more questions about fresh vs frozen embryo transfers? Our embryologists and doctors are happy to answer them. Book a consultation today!
Thank you to Samantha Pena, one of Anova’s dedicated embryologists, for providing insights into what embryo transfers look like at Anova Fertility.
References:
- Shin, J. J., Jeong, Y., Nho, E., & Jee, B. C. (2018). Clinical outcomes of frozen embryo transfer cycles after freeze-all policy to prevent ovarian hyperstimulation syndrome. Obstetrics & gynecology science, 61(4), 497–504.
- Shi, Y., Sun, Y., Hao, C., Zhang, H., Wei, D., Zhang, Y., Zhu, Y., Deng, X., Qi, X., Li, H., Ma, X., Ren, H., Wang, Y., Zhang, D., Wang, B., Liu, F., Wu, Q., Wang, Z., Bai, H., Li, Y., … Chen, Z. J. (2018). Transfer of Fresh versus Frozen Embryos in Ovulatory Women. The New England Journal of Medicine, 378(2), 126–136.
- 3. Weinerman, R., & Mainigi, M. (2014). Why we should transfer frozen instead of fresh embryos: the translational rationale. Fertility and sterility, 102(1), 10–18.
Chloe Graham (she/her)
Patient Coordinator
Master's Student (University of Guelph, Biomedical Sciences)
About the author
Chloe is a Masters Student in Biomedical Sciences at the University of Guelph, who also works as a patient coordinator at Anova Fertility.
At Anova, she educates patients through creating online resources, manages patient flow and assists with administrative functions. Before joining our team, Chloe advocated for women’s health and reproductive rights as an executive member of Oxfam at Guelph, local branch of the international anti-poverty organization.
