You are here
A Better Way to Screen Embryos for Genetic Defects: ACGH
a blog by David Kreiner, M.D., F.A.C.O.G., May 3, 2010
Pre-embryo genetic screening (PGS) was developed to help weed out embryos containing inherited metabolic disorders and genetic abnormalities prior to implantation. It was thought that PGS could be used to minimize the risk of miscarriage and perhaps even increase live birth rates in older women undergoing IVF.
We have thus far been disappointed in our results obtained using the FISH technique, the procedure performed for PGS for the past decade and a half. But an alternative new technology that was recently developed makes me very excited about PGS once again: Array Comparative Genomic Hybridization (aCGH).
ACGH is a technique actually applied to detect deficiencies and excesses of genetic material in the chromosomes. DNA from a test sample and a normal reference sample are labeled using colored fluorophores that hybridize to several thousand probes. These probes are created from most of the known genes of the genome and placed on a glass slide.
The differential color of the test compared to the normal sample DNA reflects the amount of DNA in the test specimen. It can pick up monosomies, trisomies or significant deletions on an embryo’s chromosomes.
The first baby born from this procedure was in September 2009 to a 41-year old woman. When aCGH is performed on a Blastocyst biopsy, it is effective in screening out mosaicism (mixed cell lines in the same organism). ACGH is 20 percent more sensitive than the best FISH assays with an error rate of two to four percent. Fifty percent of the embryos tested were normal with pregnancy rates exceeding Blast transfers without aCGH screening.
So, who could benefit from using this new technology?
1. Patients with repeat miscarriages can eliminate up to 90 percent of their miscarriages.
2. Older patients who naturally have a higher percentage of genetically abnormal embryos may now screen for and only transfer their normal embryos.
3. Patients who want to maximize their success with a single embryo transfer.
4. Patients who have experienced repeat implantation failure can be screened for genetically abnormal embryos.
This technology is available for about the same cost as the FISH procedure yet, since it is performed on a Blastocyst, it is safer with less effect on the integrity of the embryo and without significant risk of wrongly identifying abnormal embryos. A concern with FISH is that embryos identified as abnormal can actually result in a normal fetus. This risk is practically eliminated with aCGH and is another reason making it more successful.
I expect PGS will now become a commonly used addition to standard IVF to promote more successful single embryo transfer, improve success in older patients, eliminate miscarriages and treat patients with repeat implantation failure.
We are approaching a new era in IVF. Brace yourselves for a thrilling ride into IVF’s future.