All About Thawing Frozen Embryos

In many cases, couples decide to cryopreserve their remaining embryos after an in vitro fertilization (IVF) treatment. They could freeze the embryos right after treatment before proceeding to a transfer due to concern of ovarian hyperstimulation syndrome or high progesterone. Others cryopreserve their embryos in case their first cycle is unsuccessful or for future use. Either way, all the frozen embryos will have to be thawed in the same fashion for a FET cycle. With all the nerves and excitement come lots of questions about the thawing process.

When do you thaw the embryo?

Typically, the frozen embryo is thawed on the day of procedure. Thawing the night before could result in the embryo developing out of sync with the lining. Everything is timed accordingly, making it extremely important that directions are followed, especially consent and the desired amount of embryos to thaw.

Which embryos are selected?

The best overall quality embryos are selected first and then downward. Just because one has “A” quality and the other “B” quality or one is farther expanded than the other does not necessarily mean the B or the less expanded is bad and won’t take. It is important to remember that only embryos that are likely to aid in a potential viable pregnancy will be transferred and frozen.

What is the survival rate?

There is always a chance that the embryo will not survive a thaw due to outside factors that cannot be controlled. Typically we see around a 95% survival rate. Which is comparatively high to the alternative freezing method called slow freeze with an 86% survival rate. Aside is a picture showing an embryo that has survived the thaw and fully re-expanded. Transferring the thawed embryo prior to full re-expansion gives the embryo the chance to re-expand in the natural uterine environment.

Does freezing and thawing affect the embryo?

In some incidences, an embryo needs to be re-vitrified. Such cases occur when a couple of signs consent for 2 embryos to be thawed and transferred and then change their mind at the time of the transfer. In this situation, the extra embryo has to be frozen for later use. As long as the embryo to be re-vitrified survives the thaw, continues to expand and is of good quality the embryo can be vitrified. However, the same rules apply to the embryo; it may not survive the future thaw. Every case is different and every embryo is different. Typically with vitrification the system and protocol work very well and often times there are no problems with re-vitrification.

What is assisted hatching?

It is a procedure where a hole is made in the zona to assist the embryo to hatch out of its shell. This is done to make sure that the embryo will hatch out of its shell and is not stuck inside due to any hardening in the zona from the vitrification process. Below are pictures of embryos starting to hatch out of its shell. Once it is fully hatched the embryo is ready for implantation. Currently, at Invia Fertility Specialists, we do assist in hatching on every embryo that is thawed.