Preimplantation Genetic Screening (PGS) is performed on cells obtained from embryo biopsies in Invitro Fertilization to test for the chromosomal content in the embryos.
PGS can be performed on cells from Day 3/ Day5 embryos in IVF and tests for chromosomal aneuploidies in all the 23 pairs of chromosomes and can also detect greater than 25% of mosaicism. Using Next Generation Sequencing PGS can be performed on single cells from the embryos.
Relevance of PGS in successful pregnancy is its ability to identify the chromosomally normal embryos for transfer into the uterus by avoiding the embryo transfer in the following conditions:
In IVF as over half of all embryos can be cytogenetically abnormal, excluding these embryos from selection has improved ongoing implantation rates in some studies.
Women, in older age groups (>38 years) and those who have had repeated failure in vitro fertilisation, are more likely to produce cytogenetically abnormal embryos, which are not capable of normal development.
The chromosomes that are responsible for the major survivable aneuploidies (for example, 13, 18, 21) can be examined from an embryo biopsy using NGS.
Who should go for PGS?
PGD is testing the embryo for known genetic disorders in the parents, if either or both biological parents are affected or carriers of a specific genetic variation.
PGD is planned for people with a genetic predisposition and/or with the probability of transmitting a known genetic abnormality, families with a history of single-gene deficiencies such as cystic fibrosis, sickle cell anaemia and muscular dystrophy can be identified.
Targeted Next Generation Sequencing is performed after work up of the parents.
Who should go for PGD?
Common genetic disorders, that are tested in PGD: