Precision medicine is the precise selection of embryos and precise transfer. In precise transfer, Endometrial Receptivity Analysis(ERA) can be used to find the individual's window of implantation, so that we can transfer the blastocysts at the right time by adjusting the duration of progesterone; for precise embryo selection, we use PGT-A to find the euploidy blastocysts.

Is the PGT-A result of TE biopsy consistent with that of the ICM?

For Day5 or Day6 blastocysts, TE cells in the outer layer of the blastocyst can be biopsied. Then use the next generation sequencing (NGS) technique to amplify the whole genome of TE cells. The results of PGT-A may be euploidy(normal), aneuploidy(abnormal), or mosaic, which means chromosomes are paired in biopsied cells. However, is the PGT-A result of TE biopsy consistent with that of the ICM, which will develop into the baby in the future?

In the 2019 TSRM, a reproductive center published their research related to TE cells and ICM. First, they investigated whether the result of TE biopsy is consistent with that of the inner cell mass(ICM) in the same blastocyst. From April 2017 to June 2019, 117 blastocysts were collected from 65 patients, which were grouped by the PGT-A results of TE biopsied, divided into three groups:

1. Chromosomal abnormalities (Aneuploidy,  chromosome copy number abnormality>80%), subdivided into whole chromosomes and partial chromosomal abnormalities.

2. Mosaicism (30~80% chromosome copy number abnormality), subdivided into whole chromosome/partial chromosome mosaic.

3. Chromosome copy number is normal (Euploidy).

The result is as follows. The gray background in the table represents the consistency of the PGT-A results between TE and ICM biopsied. Only the “whole chromosome abnormality” and “euploidy” two groups have a higher consistency. The consistency of other groups was less than 30%.

Is there consistency in TE cells biopsied from different locations?

The results are as follows. In the group with "whole chromosome abnormality", the consistency rate reached 100%. In the group of "partial mosaic abnormality", it was found that there was a 54% possibility that at least the TE cell at another location was normal, and there was a 64% possibility that the ICM was normal!

Even if the PGT-A result of ​​TE cell biopsied is mosaic, the chromosomes of ICM also have a chance to be normal

Based on the above results, they came up with the following conclusions:

• The PGT-A result of TE biopsy is "partial chromosome abnormality", there is a 20% possibility that the ICM is normal.

  • When patients have no euploidy blastocysts available for transfer, implant blastocysts with "partial chromosome abnormality" may be considered.

• The PGT-A result of TE biopsy is "whole chromosome abnormality" or "whole chromosome mosaic", and all the ICM is also abnormal.

  • This type of embryo is not recommended transfer.

• Regardless of whether the PGT-A result of TE biopsy is "high or low rate fragmented chromosome mosaic," 65% of the ICM results are with normal chromosomes.

  • Embryo transfer can be considered.

Our experiences

Based on the results of this study, we reassess whether mosaic blastocysts are suitable for transfer. According to our experience, if transfer the low-rate (20-49%) mosaic blastocyst, the implantation rate is 50%； while the implantation rate of transfer high-rate (50-79%) mosaic blastocyst is 40%. It is recommended to arrange NIPS(Non-Invasive Prenatal Chromosome Screening) or amniocentesis after mosaic embryos transfer. Therefore, if there are no euploid embryos, you can choose mosaic blastocyst for transfer. Maybe it is the chance that you seize to make a miracle.