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Some patients may have more embryos than they are going to transfer in a fresh IVF cycle. We offer to freeze all appropriate embryos that remain after a “fresh” IVF cycle. Freezing embryos (cryopreservation) offers individuals the possibility of transferring these frozen embryos in a later cycle and achieving a pregnancy without having to undergo all of the steps (such as the egg retrieval) required for a fresh IVF cycle. It is important to remember that the best embryos are transferred in the fresh cycle, usually leaving embryos of lesser quality for freezing which partly explains the lower success rates seen following a frozen embryo transfer. Although the pregnancy rate may be lower, there is NO increase in your risk of a birth defect or chromosomal abnormality like Down Syndrome.
Freezing embryos requires your consent.
For patients that are undergoing a day 3 transfer, additional embryos that are not transferred will be evaluated. Embryos that are considered to be appropriate for freezing will be frozen on that day. Embryos that are felt to be delayed in their development will not be discarded. This group includes any embryo that is less than 4 cells and/or contains greater than 50% fragmentation (irregular bits of cells within the embryo).
For patients undergoing a blastocyst embryo transfer, all embryos will be cultured to the blastocyst stage (day five or six). Any non-transferred healthy embryo that has reached the blastocyst stage will be attempted to be frozen. A blastocyst is a developmentally advanced embryo. Blastocysts have a defined structure. they appear as hollow spheres with a clump of cells on one side. Part of the cells that make up a blastocyst ultimately develop into the fetus. The remainder develop into the placenta and embryonic membranes (e.g. the amnion). Blastocysts will form roughly 5-6 days after egg retrieval. Since relatively few embryos make it to the blastocyst stage, this means that there may be fewer embryos available for a subsequent frozen embryo transfer.
The cryopreservation procedure is a very complex process during which an embryo may not survive. The embryos that are to be frozen are placed in a solution containing special chemicals called cryoprotectants which help protect them during the freezing process. The embryos are then loaded into cryopreservation straws, which are labeled with the patient's name, the patient's unique IVF number, the embryos that are in the straw, and the date of the freeze. The straws are then placed in a computer controlled freezing unit. After the freezing run is completed, the straws are stored in a special tank filled with liquid nitrogen at -196 °C.
At the time of your follow-up visit with your primary physician, you will be notified regarding the number of embryos frozen. Your primary IVF physician will review with you the status of any frozen embryos that you have.
FROZEN EMBRYO TRANSFER:
During the frozen embryo cycle, no stimulation drugs are needed and there is no egg retrieval. Usually, an artificial cycle will be used with the day of the embryo transfer determined by the specific protocol. During this cycle, lupron will be used to prevent ovulation and added hormones will be given to supplement your own cycle and to improve the receptivity of the uterine lining.
THAWING PROCEDURE:
During the thawing procedure, damage from the freezing and/or thawing process can become evident. Any embryo that does not look healthy will not be transferred.
For thawing, the embryos are first warmed in a 98.6 F degree solution and the cryoprotectant chemicals are removed. Each embryo is then examined individually. All embryos that are considered healthy and viable are kept in the incubator overnight. The next day the embryos are again inspected for their status and an appropriate number of healthy embryos are transferred. Since the embryos are examined for viability again the morning of the transfer, the final number and status of the embryos available for transfer will not be known until that morning and will be reviewed with you when you arrive for your transfer. The procedure for the embryo transfer in a frozen cycle is the same as the one used in the fresh cycle.
