What is an Embryo Transfer?
An embryo transfer is the last stage in the IVF process, where the fertilized egg that has been left to grow for several days is placed in the woman’s uterus where it will hopefully implant, become a fetus, and result in the birth of a healthy child.
The embryo transfer procedure is done by loading the IVF embryo into a catheter, which is then passed through the woman’s vagina and cervix, and deposited in the uterus. Anesthesia is usually not necessary, but valium may be used.
Types of Embryo Transfer:
There are many “types” of embryo transfers though the basic principle remains the same.
Fresh Embryo Transfer
Just as the term implies, a fresh embryo transfer is the transfer of (an) embryo(s) that has not been frozen.
Frozen Embryo Transfer (FET)
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 (Day 3) Stage Embryo 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 are 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 CNY, we generally recommend transferring a day three embryo if there are less than four embryos on day one.
Blastocyst (Day 5) Stage Embryo Transfer
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 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.
Single Embryo Transfer (SET or eSET)
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.
Multiple Embryo Transfer
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. Transferring a high number of embryos (or even more than one in some instances) can get a clinic shut down in today’s day and age.
What to Expect During Embryo Transfer?
Embryo transfers take place under sterile conditions, usually in a designated transfer room at the fertility clinic. Your doctor, a nurse, the embryologist, (and your partner) will be with you. Anesthesia is usually not necessary, but a muscle relaxer or Valium is often used to help calm nerves and relax the smooth muscles of the uterus. You should take any medications that have been prescribed for you exactly as instructed. You may be asked to refrain from taking anything that is inserted vaginally (like a suppository) the morning of the transfer.
Prior to the transfer, the doctor and embryologist will confirm your name and date of birth to make sure it matches identifying information on the embryos. Then, with the assistance of the embryologist, the embryo is loaded into the transfer catheter. Around that same time, a speculum is placed into the vagina to allow visualization of the cervix, which will then be cleaned. The catheter is placed through the cervix and into the uterus using ultrasound guidance. Once in place, the embryo is gently deposited into the uterus, where it will hopefully implant.
Embryo transfer is very similar to having a pap smear. It should not hurt, but you may feel some minor discomfort when the speculum is inserted or when the catheter is passed through your cervix.
The patient is allowed to rest for about 15 minutes afterward. Follow-up instructions are given, and bloodwork is scheduled for 4-7 days post transfer and a pregnancy test for ten days post transfer.