A photograph of a lab tech removing a vial from a container filled with liquid nitrogen.

Fresh Embryo Transfer vs Frozen Embryo Transfer 

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Fresh Embryo Transfer vs Frozen Embryo Transfer

When embryos are frozen and then thawed for transfer, this is referred to as a frozen cycle. A frozen embryo transfer occurs in a non-stimulated cycle, and we can use a more natural estrogen and progesterone combination to prepare for the implantation. A fresh treatment cycle is a stimulated cycle, where multiple follicles are created. When the eggs are retrieved and the embryos created, the transfer must take place shortly after the retrieval, and according to the patient’s hormone levels.

Benefits of a Frozen Embryo Transfer

Pregnancy Rate:

Today, the technique for freezing embryos is extremely reliable, so much so that fresh and frozen embryos have the same possibility of success. At TRIO, our pregnancy rates between fresh and frozen are equivalent, and in certain cases, such as cycles that are at risk for OHSS, the pregnancy rate of frozen embryos is higher.

OHSS Risk Reduced:

One of the most important reasons we may recommend a frozen embryo cycle over a fresh one is if the patient is at elevated risk for OHSS, or Ovarian Hyper Stimulation Syndrome, a rare but serious side effect that may happen when medication stimulates too many eggs in one cycle.  In that case, choosing a frozen embryo transfer cycle will reduce this risk by removing high levels of the hormones (hCG) that could act as triggers during the transfer portion of the cycle, and opting to freeze the embryos for transfer in a subsequent cycle.

Estrogen Levels:

If a patient’s estrogen levels are very high during a cycle and the patient produces, for example, 10 follicles or more, their progesterone will be higher as well. This may affect the successful implantation of the embryo. However, if we freeze the embryos and transfer them in a subsequent cycle when the patient’s hormone levels are more like they would be in a natural cycle, the chances of that embryo implanting in the uterus are much better.


A frozen embryo transfer offers the patient more flexibility, as the patient can schedule the day they want their transfer and book their own TRIO doctor to do the procedure. A frozen transfer may also be less stressful, as only one or two ultrasounds are required, so the patient does not have to come to the clinic as often.

Safe Storage of Embryos:

Frozen embryos are stored safely and securely in tanks of liquid nitrogen. These remain in the TRIO lab under carefully controlled temperatures. Vitrification has been around clinically for about 15 years, and embryos that have been frozen over that time period and then thawed have been viable. At TRIO, all embryos that have been frozen are always checked for their viability once they are thawed and before they are implanted.

Benefits of a Fresh Embryo Transfer

The Transfer takes Place Within the Cycle:

After the retrieval, the egg is fertilized in our lab and the embryo grows to the Blastocyst or day 5 stage, which is optimal for transfer. A fresh transfer occurs at the Blastocyst stage – that is 5 days after your retrieval.

Faster results:

Because the fresh transfer must take place 5 days after the retrieval, the entire cycle, from day 1 to transfer, is approximately 4 to 6 weeks.

Providing the opportunity for a transfer:

Unfortunately, not all embryos are capable of becoming Day 5 blastocysts in the lab. If our embryologists think a patient’s embryos are viable but may not make it to the blastocyst stage, we will recommend a fresh transfer on or around Day 3. This is a very rare occurrence in our lab,  however can be an option in rare cases.

Fresh Embryos Can be Frozen for Additional Transfers:

Most cycles result in more than one embryo. At TRIO, in most cases, our policy is single embryo transfer, therefore all surplus embryos are safely frozen at the blastocyst phase in case the patient decides to transfer them in a subsequent frozen cycle.

Please ask your TRIO doctor about both of these options to find out which one is right for you.