Definition - What does Pre-Embryo mean?
Pre-embryo is a term used to describe the fertilized egg before implantation has occurred. The term embryo is sometimes used to refer to a pre-embryo, but technically speaking an embryo exists only after implantation in the uterus. Pre-embryos created using in vitro fertilization (IVF) can be frozen for later transfer.
FertilitySmarts explains Pre-Embryo
After an egg has been fertilized by a sperm it is known as a pre-embryo. Normally, the pre-embryo will continue to divide over the next several days as it makes its way down the fallopian tube into the uterus. Once it successfully implants in the uterine wall, it is referred to as an embryo. It is called an embryo from implantation until the 8th week of gestation. At the end of the 8th week, the embryo becomes a fetus and remains in this stage until birth.
If an individual or couple has opted to freeze embryos this will be done at the pre-embryonic stage. Typically, the pre-embryos are allowed to develop for 3-5 days before they are frozen. Prior to freezing, pre-embryos are graded for quality. If they appear to be of poor-quality or the cells have stopped dividing at this time, they will not be frozen as they are unlikely to survive the freezing process and result in a successful pregnancy.