• An embryo transfer is a final stage in the In Vitro Fertilization (IVF) process where the fertilized egg—now an embryo—is placed in the woman’s uterus.
• The embryo is loaded into a catheter, which is passed through the vagina and cervix and into the uterus where it is deposited.
• This generally takes place between 3 and 5 days after egg retrieval if having a fresh transfer and anywhere from 4 weeks to years later if doing a frozen transfer.
• There are many different types of embryo transfers: fresh, frozen, cleavage (day 3), a blastocyst (day 5), single, and multiple embryo transfers.
• Today’s standard practice is to transfer one embryo (occasionally two) embryo(s) at a time.  This minimizes the chance of multiples while maintaining the same cumulative live birth rates (per retrieval) form an IVF cycle. Any remaining embryos from the IVF cycle are either frozen (if the first transfer is with fresh embryo) or remain frozen (if the first transfer if a frozen transfer – also called a freeze all cycle).

Just as the term implies, a fresh embryo transfer is the transfer of (an) embryo(s) that has not been frozen.

A Frozen Embryo Transfer is a cycle in which frozen embryos from a previous IVF or donor egg cycle are thawed and then transferred into a woman’s uterus.

A frozen embryo transfer may be done for a number of reasons:

Medically Advised Due to Uterine Receptivity: During an IVF cycle, a woman is in a state of controlled ovarian hyperstimulation, which adds a good deal of physiological stress to the woman’s body.  In some cases, the woman’s body is unable to simultaneously prepare a beautiful “home” for the embryos to be transferred. If the woman has ovarian hyperstimulation syndrome or has elevated progesterone or estrogen levels or has a lining under 7mm at the time of trigger, it may be advised to do a “freeze all cycle,” followed by a FET.  This allows the intended mother to wait until the uterus/endometrium is more receptive and implantation more likely.

A Second Embryo Transfer: In a conventional IVF cycle, it is common for 10-15 eggs to be produced through controlled hyperstimulation and result in a number of high-quality embryos available for transfer. Today’s standard practice is to transfer one (sometimes two) embryo into the woman’s uterus and freeze all remaining embryos to increase the chance of future pregnancy (should the couple want to continue expanding their family after giving birth or if the first transfer fails).

Easier to plan: Because there are times when it is medically advised to convert a fresh cycle to a freeze all cycle with an FET, many, particularly travel clients, find it much easier to plan in advance for a frozen transfer as they are rarely ever canceled, can be easily planned, and offer comparable success rates as a fresh transfer.

Cleavage stage embryos are called such because the cells in the embryo are dividing (or cleaving), but the embryo itself is not growing in size. This stage is usually reached around day three but may happen on day two or four.  They have often referred to simply as “day three embryos.”

Some fertility experts believe there’s no substitute for a woman’s uterus and that embryos should be put back into the uterine environment as quickly as possible. Since not all embryos survive until Day 5, transferring on Day 3 is a way to ensure an embryo gets to the optimal environment to thrive.  At Dr.INVITRO, we generally recommend transferring a day 5 embryo to select best quality embryo.

A blastocyst is an embryo that has developed into a single-layered sphere of cells encircling a fluid-filled cavity with a dense mass of cells grouped together.  Blastocysts contain anywhere from 60 to 120 cells.  This usually occurs on day five, but may happen on day 6, 7, or even 8. By this stage, the embryo has differentiated into two cell types:  the trophectoderm, the cells on the periphery of the embryo that forms the placenta, and the inner cell mass (ICM), the dense mass of cells on the inside that forms the fetus if the embryo implants.

A blastocyst embryo is considered to be more “special” than an earlier stage embryo since it has a higher probability of being genetically normal, implanting, and leading to a live birth than a cleavage-stage embryo.

By delaying embryo transfer to the blastocyst stage, an embryologist is better able to select embryos with a higher probability for continued development.

An embryo that is grown to a blastocyst stage can also be genetically tested prior to transfer which can help reduce the risk of miscarriage for some populations, avoid known genetic disorders, and select the sex of the child.

A(n) (Elective) Single Embryo Transfer is the practice of transferring only one embryo into a woman’s uterus. This offers a reduced chance of multiples while maintaining a very similar rate of pregnancy. Due to the reduced risk of an eSET along with having a very similar rate of pregnancy, eSET has quickly become the gold standard practice for transferring embryos with an IVF procedure.

A transfer of multiple embryos is quite simply the transfer of more than one embryo. While this can be done for some, there are strict guidelines that restrict the transfer of multiple embryos.