Natural selection between day 3 and day 5/6 PGD embryos in couples with reciprocal or Robertsonian translocations
For translocation carriers, preimplantation genetic diagnosis (PGD) provides the opportunity to distinguish between normal/balanced and unbalanced embryos prior to implantation and, as such, increases the likelihood of a successful ongoing pregnancy. The data presented here compares autosomal reciprocal and Robertsonian translocation segregation patterns in day 3 versus day 5/6 IVF-PGD embryos to determine if there is a difference in the chromosome segregation patterns observed at these developmental time points.
A retrospective analysis on PGD translocation carriers at Monash IVF was performed. Segregation patterns were compared between day 3 and day 5/6 embryos to ascertain whether selection against malsegregants exists.
For reciprocal translocations, 1649 day 3 embryos (139 translocations) from 144 couples and 128 day 5/6 embryos (59 translocations) from 60 couples were analysed. Day 3 segregation analysis showed that 22.3% of embryos were normal/balanced (consistent with 2:2 alternate segregation) and 77.7% were unbalanced (malsegregation). Day 5/6 segregation analysis showed that 53.1% of embryos were normal/balanced and 46.9% were unbalanced. For Robertsonian translocations, 847 day 3 embryos (8 translocations) from 54 couples and 193 day 5/6 embryos (6 translocations) from 31 couples were analysed. Day 3 segregation analysis showed that 38.7% of embryos were normal/balanced (consistent with 2:1 alternate segregation) and 61.3% were unbalanced. Day 5/6 segregation analysis showed that 74.1% of embryos were normal/balanced and 25.9% were unbalanced.
This data demonstrates an increase in the proportion of genetically normal/balanced embryos at day 5/6 of development. This suggests a strong natural selection process between day 3 and day 5/6 in favour of normal/balanced embryos. These findings support performing PGD testing on day 5/6 of embryo development.
KeywordsPreimplantation genetic diagnosis Reciprocal translocation Robertsonian translocation Segregation Unbalanced embryos
The authors would like to thank all the embryology staff at Monash IVF for performing the embryo biopsy procedures and the genetics staff at Monash IVF for their genetic analysis and contributions towards this paper.
Claire E. Beyer participated in study concept and design, data acquisition, study execution, analysis, manuscript drafting, critical discussion and interpretation of data.
Elissa Willats participated in study design, manuscript drafting, critical discussion and interpretation of data.
Compliance with ethical standards
This study was approved by the Monash Surgical Private Hospital Human Research Ethics Committee (approval number: 07078).
Conflict of interest
The authors declare that they have no conflict of interest.
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