Pre-implantation genetic testing for aneuploidy (PGT-A)

Abstract

© 2020 Royal Thai College of Obstetricians and Gynaecologists. All rights reserved. Preimplantation genetic diagnosis (PGD) or embryo selection was first performed in 1989 using PCR for gender selection to avoid X-linked recessive disorder. However, there was a misdiagnosis due to allele drop out (ADO). Therefore, fluorescent in situ hybridization (FISH) was recommended for gender selection and detection of chromosome abnormalities and PCR was for monogenic disorders. Since then, a number of advanced modern analysis methods for preimplantation genetic testing (PGT) of chromosome balance were developed. A more sophisticating comparative genomic hybridization microarray (aCGH) was introduced in 2011 providing detailed copy number variation (CNV) of 24 types of chromosomes (22 pairs, X and Y). A single aCGH protocol was used for PGT of aneuploidy (PGT-A) and PGT of segmental rearrangement (PGT-SR) for every chromosome in one go. Next generation sequencing (NGS) replaced aCGH in 2015 due to its better resolution and lower cost. Single nucleotide polymorphism microarray (aSNP) with karyomapping analysis for simultaneous PGT of monogenic disorders (PGT-M) and PGT-A is still more expensive. In this article, various embryo biopsy and chromosome analysis techniques are discussed. The pros and the cons of each techniques are also included.