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What is an embryo transfer?

An embryo transfer is a part of IVF procedure in which a fertility specialist uses an ultrasound to guide a catheter containing the IVF-produced embryo(s) to transfer the embryo(s) directly into the uterus. The process of embryo transfer takes only a few minutes. The process does not involve anesthesia and only short recovery period is required. Prior to the transfer, embryos are graded and the type of grading depends on the stage of the embryo. For cleavage stage embryos, typically on day three, the number of cells and a grade (A – D) will be assigned. For blastocysts, there will be a number and two letters assigned. The number refers to the amount of expansion of the fluid (the “cyst”) in the blastocyst. The two letters (A – D) that follow refer to the inner cell mass (destined to become the baby) and the trophectoderm (destined to become the placenta), respectively. Cells from an embryo can also be tested for genetic anomalies prior to an embryo transfer. Scientists have a choice of two genetic tests for embryos. In preimplantation genetic diagnosis (PGD), an embryologist removes a group of cells to test for a specific genetic abnormality, such as cystic fibrosis. Preimplantation genetic screening (PGS) tests for the proper makeup in all chromosome pairs, as missing or additional chromosomes lead to disorders and diseases. An example of such a disorder is Down syndrome, in which there is an extra chromosome in pair number.

Types of Embryo Transfer

Blastocyst Transfer

A blastocyst transfer includes developing embryos in a laboratory for five days before transferring them into the uterus. When the embryo has reached the blastocyst stage (day five), it is more fully developed with multiple cells. At this point the embryo resembles the stage of a natural embryo when it enters a uterus for implantation, which increases the chances of attaining a successful pregnancy. However, it is not necessary that all embryos are able to develop to the blastocyst stage. Studies show that blastocyst transfers result in higher implantation and pregnancy rates as compared with cleavage stage embryos. Blastocyst transfers may be of particular benefit for patients who develop many good quality embryos, who have failed to achieve a pregnancy with a day three transfer in the past, or who have poor quality embryos at day three.

Cleavage Stage Embryo Transfer

A cleavage stage embryo transfer refers to embryos that are transferred at an earlier stage of development when they have fewer cells, typically six to eight, and occurs on day two or three after fertilization. Cleavage refers to the division of the cells in an early developing embryo. Cleavage stage embryo transfer is a good option for patients who have fewer good quality embryos. Also, transfer on day three is less risky than allowing the embryos to go to day five.

When Embryo Transfer is Needed

IVF and embryo transfer is required in cases where there is difficulty in natural conception or difficulty occurring. There are many reasons for embryo transfer, including:

  • Ovulation disorders: If ovulation is infrequent, fewer eggs are available for successful fertilization.
  • Damage to Fallopian tubes: The Fallopian tubes are the passageway through which the embryos travel to reach the uterus. If the tubes become damaged or scarred, it is difficult for fertilized eggs to safely reach the womb.
  • Endometriosis: When tissue from the uterus implants and grows outside of the uterus. This can affect how the female reproductive system works.
  • Premature ovarian failure: If the ovaries fail, they do not produce normal amounts of estrogen or release eggs regularly.
  • Uterine fibroids: Fibroids are small, benign tumors on the walls of the uterus. They can interfere with an egg’s ability to plant itself in the uterus, preventing pregnancy.
  • Genetic disorders: Some genetic disorders are known to prevent pregnancy from occurring.
  • Impaired sperm production: In men, low sperm production, poor movement of the sperm, damage to the testes, or semen abnormalities are all reasons natural fertilization may fail.

What to Expect before, During, and After an Embryo Transfer

Around 2 or 3 days before the embryo transfer, the doctor will choose the best eggs to transfer to the womb. There are many processes available to aid selection, though non-invasive methods such as metabolomic profiling are being tested. Metabolomic profiling is the process of selecting the most beneficial eggs based on a number of different factors. This could limit the need for invasive procedures in the future. These eggs will then be fertilized in a lab and left to culture for 1-2 days. If many good quality embryos develop, the ones that are not going to be transferred can be frozen.

After the Embryo Transfer

A follow-up appointment after 2 weeks to check if the embryo has implanted well and the transfer was successful. After the procedure of embryos transfer, women may experience some cramping, bloating, and vaginal discharge.