We turned to Dr Izuierdo, fertility expert, director of Vida Fertility Alicante and asked him to help us understand what it means when when people talk about a frozen transfer vs. a fresh transfer
A frozen transfer, aka delayed or deferred transfer, emerged as an alternative option to a fresh transfer in assisted reproductive treatments using IVF, with the aim of avoiding the negative effects that ovarian stimulation may have on the endometrial receptivity, while also reducing the risk of ovarian hyperstimulation.
Let’s start with the basics… What is a deferred transfer?
A deferred transfer is an embryo transfer that is not done in the same cycle as the stimulation cycle. Therefore, it involves transferring an embryo that has been vitrified after its development in the laboratory. In contrast to a fresh transfer, where the embryo is transferred to the maternal uterus shortly after reaching the blastocyst stage, 5 or 6 days after ovarian puncture and fertilization.
On which day of the cycle is the deferred transfer performed?
The day of the cycle only matters when a deferred transfer is done in a natural cycle, and in this case, it would be approximately on day 21. In a substituted cycle, controlled by hormonal treatment, the day of the cycle is irrelevant because what really matters is how many days of progesterone the patient has received before the transfer; ideally 5.5 days.
Which is better, fresh embryo transfer or frozen embryo transfer?
New studies increasingly advocate for deferred transfers, citing higher implantation and live birth rates. This is probably due to the fact that the embryo development and the implantation window do not always synchronize for all women. Some embryos may need more than 5 days to reach the state of blastocyst, and it is beneficial to wait until they reach their optimal state before transferring. Conversely, some patients have displaced implantation windows, and for them, 5.5 days of progesterone are not ideal for a proper embryo implantation. For both examples (and more), a fresh transfer would be inappropriate.
What is the success rate for both fresh and frozen transfers?
With the advances of vitrification techniques, the type of transfer no longer interferes with success rates. The success depends on the type of treatment, patient’s age, whether using own eggs or egg donation, the stage of embryo development (day 3 or day 5), whether a genetic euploidy test has been performed, if the transfer was done at the right time, etc. There are multiple factors that determine success rates more than the type of transfer. In fact, nowadays, this distinction is almost no longer seen in statistics.
How many consecutive frozen embryo transfers can be done?
As many consecutive transfers can be done as necessary or as many embryos are available for it. In general terms, a failed transfer corresponds to one cycle for a woman. However, in practice, we also need to determine the cause of failure to see if there is anything we can do to address it for the next transfer. For example, if the implantation window is displaced, if there is an immunological factor… Some tests may need to be performed, making consecutive transfers not as immediate. Finally, we know that emotional aspect plays a significant role in assisted reproduction, and we won’t proceed with a new transfer if the patient doesn’t feel prepared for it.
Can a deferred transfer be canceled?
Certainly, yes. In fact, it should be done if the conditions are not optimal. That’s why we always advise verifying the endometrial stage prior to the transfer to avoid unnecessarily thawing the embryo.
Can it be done in a natural cycle or a substituted cycle?
Both options are possible, and the decision should depend on which conditions are better for the patient in terms of endometrial thickness and progesterone levels. In general, to reduce stress and better align the transfer cycle with their personal life, patients and clinics opt for a substituted cycle.