Authors: Sergei Evsikov, PhD., David Hill, PhD., Mark Surrey, MD., and Hal Danzer, MD. Beverly Hills, California
Objective: The major weakness of Preimplantation Genetic Testing is a questionable reliability of the results, based on the analysis of a single cell. Biopsy of more than one blastomere should increase the efficiency and reliability of PGD analysis, but only at the price of lowering embryo viability.
Design: A retrospective clinical study.
Setting: Private clinic for assisted reproductive technology.
Patients: Patients undergoing IVF-PGD cycles for the purpose of aneuploidy testing.
Intervention: Each Day 3 embryo from IVF-PGD patients had undergone a biopsy of a single or multiple (usually two, “non-sister”) blastomeres (BB). FISH technique was used to analyze chromosomes 13, 18, 21, X, and Y. If the first round of BB-FISH gave questionable results, the corresponding embryos had undergone second round of BB-FISH in the late afternoon of Day 3. Genetically normal embryos were transferred on Day 4 to establish a pregnancy; the rest were fixed on Days 4 to 7.
Main Outcome Measures: Negative effect of a single vs. multiple blastomeres biopsy was correlated with the embryo ability to establish a pregnancy or, in the case of genetically abnormal embryos, to reach blastocyst stage in vitro.
Results: Biopsy of two blastomeres revealed embryos which otherwise would have given “false positive” results: even the embryos with Down’s syndrome can be left undetected if PGD is based on the analysis of a single blastomere. These cases should justify the biopsy of two blastomeres as a standard practice for PGD.
There was no decrease in the cell number at the blastocyst stage or the rate of blastocyst formation among the embryos with more than one blastomere biopsied. The average number of blastomeres biopsied from the embryos which established pregnancies was 1.6; the embryos which failed to implant had on average 1.3 blastomeres biopsied.
Conclusion: Although preliminary, our data suggest that biopsy and analysis of two blastomeres from the embryos being at the advanced cleavage stage (8 to 16 cells) is superior to a single blastomere biopsy from a 6-10 cell stage embryo.