With trophectoderm biopsy, a small group of cells (usually 5 to 10) is removed from the trophectoderm of a blastocyst.
A blastocyst is made up of 2 different cell types, the inner cell mass (ICM) and the trophectoderm. The ICM cells develop into the fetus while the trophectoderm cells are the embryonic cells that go on to develop into the embryonic side of the placenta.
For the procedure, a laser is used to create a small opening in the zona pellucida (the shell of the embryo) surrounding the embryo on day 3 of development. This allows the embryo to begin the hatching process early on day 5 of development, which is slightly earlier than it may normally occur. With hatching, a portion of the trophectoderm begins to herniate through the zona pellucida. Using micro tools, the embryo is held and 5 to 10 cells of the herniating portion of the tropectoderm removed from the embryo again using a laser. A normal blastocyst is made up of 100 or more cells, so removing these cells has no effect on the further development of the embryo. Also, by removing cells from the trophectoderm only, the ICM is not disturbed. Because not all embryos develop at the same rate, some embryos may be biopsied on day 5 while others will be biopsied on day 6.
After the biopsy, all biopsied embryos are immediately vitrified. The removed cells are shipped to the testing laboratory. Once our IVF lab receives the results of the genetic testing, the patient can undergo a frozen embryo transfer. The normal embryos will be thawed and transferred to the patient’s uterus.
Trophectoderm biopsy can be beneficial over day 3 biopsy for a select group of patients.
One case where this may be advantageous is the instance where a patient has many embryos and would like to limit the number biopsied. There will be some embryos that will not form blastocysts, so by doing a day 5 biopsy, only the embryos that have the capacity to form blastocysts will be biopsied. Trophectoderm biopsy is also a choice for patients who have previously frozen blastocysts that were not genetically tested, but there is reason to do so now. Also, day 5 biopsies can be used to confirm results from day 3 biopsies or in the cases where an inconclusive result is obtained from the day 3 biopsy.
Vitrification is an essential part of the trophectoderm biopsy process. With the excellent survival rates we have achieved using vitrification, freezing embryos for a later transfer, after results have been received is a viable option. Even in cases where we perform trophectoderm biopsy on thawed embryos, they can be successfully re-vitrified and transferred during a later frozen embryo transfer cycle.