How Are Embryos Frozen?
Some women who are undergoing fertility treatment have embryos left over after the first cycle. To avoid wasting these, you can have them frozen, to be used in later cycles if desired. Only the highest quality embryos will be chosen for freezing. Embryos can be frozen at several different stages of development such as when they are comprised of a single cell or when they have divided into two to eight cells. They can also be frozen at their blastocyst stage, which they reach five days after fertilization.
The embryos will be placed in a protective substance which replaces the water in the cells and prevents ice from forming and causing damage. They will then be frozen using either a slow cooling method or a fast-freezing method. Once frozen, they will be stored in liquid nitrogen until ready for use.
When can you do a frozen embryo transfer?
Once embryos have been frozen, they will remain viable indefinitely. You can choose to begin a frozen embryo transfer after an unsuccessful fresh in vitro fertilization (IVF) cycle if you still wish to start a family.
How long do frozen embryos take to implant?
Unlike fresh embryos, which usually implant within one or two days after a blastocyst transfer, frozen embryos take a little longer to implant. Usually, they implant within five days. This is referred to as late or delayed implantation. This slight delay has several advantages, including:
- Giving the uterus time to recover from the effects of IVF the medications used to stimulate egg production.
- Allowing time for genetic screening, increasing success of a healthy birth.
- Reducing the risk of ovarian hyperstimulation syndrome (OHSS), which is a risk when using fresh embryo transfers.
- If undergoing multiple transfers, frozen embryo transfers are less expensive than repeated fresh embryo transfers.
Frozen embryo transfer implantation does take slightly longer. Typically an at home pregnancy test is performed around ten to twelve days after the transfer to see if it has been successful.