Evaluation of chromosomal constitution in choronic villi samples of aborted fetuses after embryo transfers of euploid blastocysts

Abstract

Introduction Preimplantation genetic testing of aneuploidies (PGT-A) using Next Generation Sequencing (NGS) platforms decreases significantly the risk of abortion from aneuploidy reason, nevertheless some fetuses are unfortunately aborted despite PGT-A from another sakes. NGS platforms provide high dynamic range and are able to detect copy number variations starting at 20% mosaicism. Material of trophectoderm biopsy includes several trophectoderm cells and it is quite often discussed whether such sample is representative enough to reflect the inner cell mass chromosomal status. The aim of this retrospective study is to reveal a representativeness and a significance of a trophectoderm biopsy sample evaluation with respect to the chromosomal constitution during the further embryonic development and assignments of concordance between trophectoderm biopsy day 5-6 and the finding in chorionic villi of aborted fetuses. Material and methods 59 chorionic villi samples were obtained from aborted fetuses during the surgical curettage for incomplete spontaneous or missed early abortions during a period January 2016 till March 2018. All samples were cleaned, washed and stored in a phosphate buffer and after DNA isolation the chromosome copy number was evaluated using 24sure array (Illumina). 42 samples were obtained from fetuses conceived after embryo transfers, 10 embryos were transferred without PGT-A and 32 were analyzed using PGT-A (VeriSeq™ PGS Kit by Illumina) before an embryo transfer. In all study cases a single embryo transfer was performed. All 32 PGT-A embryos were originally diagnosed as euploid. 17 samples were derived from spontaneously conceived embryos. The samples were divided into 3 groups. Group A consists of 10 non-PGT-A samples, group B of 17 samples from spontaneously conceived fetuses and group C of 32 samples from fetuses after PGT-A. Results In total, 23,7 % (14/59) chorionic villi samples were diagnosed as aneuploid. In the group A (non-PGT-A fetuses) 50% (5/10) were aneuploid, in the group B (spontaneous conceptions) 47% (8/17) samples were aneuploid while in the group C (PGT-A fetuses) only 3% (1/32) were aneuploid. Euploid status was concordant in 31 out of 32 PGT-A analyzed embryos (97%). Conclusions Our retrospective study showed that 50% of aborted fetuses after IVF with no PGT-A were aneuploid. This corresponds very well with the aneuploidy rate observed for products of spontaneous conception in infertile couples (47%). Chorionic villi samples from aborted fetuses derived from previously negatively tested blastocysts were aneuploid in 3% of cases (1/32). The concordance between an euploid status of trophectoderm samples and chorionic villi tissue from aborted fetuses is 97%. This confirms the figures referred previously in another studies comparing evaluation of trophectoderm and inner cell mass of the embryo and fully supports routine implementation of PGT-A into assisted reproductive techniques. The slight discordance is possible to be explained by unequal distribution of aneuploid/mosaic cell lines within the trophectoderm tissue at the blastocyst stage when the biopsy is performed.