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Trophectoderm Biopsy Video - PGD Testing and IVF
Improved Method for Embryo Testing with Preimplantation Genetic Diagnosis and Screening, PGD and PGS
Page author Richard Sherbahn MD
What is trophectoderm biopsy?Trophectoderm biopsy involves removing some cells from the trophectoderm component of an IVF blastocyst embryo. The removed cells can be tested for chromosome normality, or for a specific gene defect using PGS or PGD genetic testing.
What is blastomere biopsy?
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Video showing trophectoderm biopsy for PGD (30 seconds)
Picture of a high quality blastocyst 5 days after fertilization
The cells in the 10 o'clock area comprise the inner cell mass (ICM) - precursor of the fetus
Trophectoderm cells (TE) that will form the placenta surround the fluid cavity
What is PGD vs. PGS?
- Preimplantation genetic diagnosis, PGD, involves testing done on in vitro fertilization IVF embryos prior to transferring them to the uterus
- The term PGS (preimplantation genetic screening) is often used when referring to testing done looking specifically at chromosome abnormalities (karyotype testing)
- The term PGD would often be used when referring to looking for specific gene defects in the DNA code
- For example, PGD could be done on embryos from a couple with both partners known to be carriers for a specific genetic disease (such as cystic fibrosis, etc.)
Negatives about blastomere biopsy on day 3
- On day 3 human embryos usually have about 6-10 cells. The cells are large and have significant cell to cell attachments.
- Therefore, blastomere removal requires a large hole in the shell - and that cell must be pulled (torn) away from its neighbors
- Depending on the total cell number, about 1/6 to 1/10 of that embryo has been removed (if only 1 cell is taken)
- The embryo gets somewhat "beat up" and loses a significant part of its total mass
The blastomere removal procedure on day 3 is traumatic to the embryo and has been shown to reduce its developmental potential (strength). Therefore, day 5 trophectoderm biopsy at the blastocyst stage has been tried in order to minimize trauma.
Advantages of trophectoderm biopsy and PGD success rates
- The advantage of trophectoderm removal is that the embryo is much less traumatized by the procedure compared to blastomere removal done on day 3
- Since the embryo has many more cells (about 100) at the blastocyst stage than on day 3 (about 6-10), we can remove multiple cells from the trophectoderm with very little impact
- Trophectoderm biopsy allows the potential to increase IVF live birth success rates by screening for chromosomally normal embryos prior to transfer back to the uterus
- Well controlled studies of blastomere biopsy have repeatedly shown lower IVF success rates as compared to IVF without any cell removal
- There are not yet published controlled studies comparing IVF with trophectoderm removal versus IVF without cell removal
- Such studies are needed and will likely be done soon
Disadvantages of trophectoderm biopsy
- At this point performing the genetics techniques for chromosomal or genetic analysis on the cells requires 24-48 hours
- So a day 3 biopsy can be done with the information about the chromosomes or genetics coming back in time to do transfer on day 5 with fresh embryos
- However, when the cell removal is done on a day 5 embryo the genetic or chromosomal results will not be back in time to do a fresh transfer procedure
- So we must do the trophectoderm removal, then freeze the embryos, and wait to get the genetics results back before we thaw and transfer back blastocysts to the uterus
- The disadvantages of this approach are:
- Increased cost from adding a frozen embryo transfer cycle
- Delay of about a month before the transfer can be done
- The need for development to the blastocyst stage to do a biopsy procedure. Not all couples will have embryos develop to blastocyst stage.
How is trophectoderm biopsy done?
- See the video above on this page
- First we wait until the embryo has developed to the expanded blastocyst stage
- A very small hole is made in the outer shell of the embryo with a laser
- A pipette is used (with help from the laser) to detach a few cells off of the trophectoderm component - the precursor to the placenta (see blastocyst picture above)
- The cells that will become the fetus itself (inner cell mass) are not disturbed
- After trophectoderm removal, all biopsied embryos are frozen
How is preimplantation genetic screening, PGS, done with blastocyst IVF embryos?
- Trophectoderm removal is done as described above
- The biopsied trophectoderm is sent off for chromosomal (and/or genetic) analysis
- The chromosomal (or genetic) test results come back within several days
- The appropriate embryos are thawed and transferred back to the uterus in a frozen transfer cycle
It is quite possible that in the future technology will advance so that we can assess chromosomal competence and/or genetic specific genetic defects within a few hours. This would allow day 5 trophectoderm removal with transfer of fresh embryos the same day. For now that is not practical so we use trophectoderm biopsy, embryo freezing and then embryo thawing and transfer in another month.
We are currently offering trophectoderm biopsy and embryo freezing (vitrification) and subsequent frozen transfer for cases needing genetic evaluation for single gene defects or for couples that want testing for normalcy of chromosomes (aneuploidy screening).
See our costs for preimplantation genetic screening
Eventually, studies will be done and published that will determine whether preimplantation genetic screening truly increases chances for pregnancy and live birth with IVF for couples with advanced maternal age, recurrent IVF failures and/or recurrent pregnancy loss.
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