Pre implantation genetic screening includes PGT – A ; PGT – M and PGT- S 

Pre implantation genetic screening for aneuploidies (PGT – A)  is a screening test to check if any genetic or chromosomal abnormality is present in the embryos created through IVF/ICSI before  the embryo is transferred. Chromosomal aneuploidy is one of the major causes of infertility, maternal age-related lower pregnancy rate and IVf failure. PGT – A helps to identify and transfer chromosomally normal embryos. It thus shortens the time to pregnancy by reducing the need of multiple IVF cycles. Transfer of chromosomal normal embryos also results in higher pregnancy rates. It also reduces the miscarriage rates. 

Indications of PGS- 

1) Advanced maternal age

2) Recurrent miscarriages

3) Recurrent IVF failures – Two or more IVF failures

Preimplantation Genetic Testing – Monogenic  ( PGT – M ) is  used to identify known genetic defects within embryos. This technique is used to prevent certain genetic diseases or disorders from being passed on to the child when 1) one or both the parents have a known genetic disease or disorder that can result in genetic disease in the child 2) couple already has an affected child so that a healthy offspring can be born. Some examples are  carriers of chromosomal disorders, Sex linked genetic disorders, Single gene disorders, beta thalassemia, Duchenne muscular dystrophy, neurofibromatosis, sickle cell anemia, cardiac disorders,  carriers of BRCA1 etc. 

Preimplantation Genetic Testing – structural rearrangement ( PGT- SR ) – This procedure is used to test embryos that are at risk for chromosome gains and losses related to parental structural chromosomal abnormalities (eg, translocations, inversions, deletions, and insertions)

In PGS cycles following the process of egg retrieval and fertilization the embryos are allowed to grow in the lab for upto 5 days ( blastocyst stage). A biopsy of  few cells is then taken and sent for genetic testing. Usually it takes few days for the results of the tests to be available, so all the biopsied embryos are frozen. Once the chromosomally normal embryos are identified they are transferred into the uterus via a frozen embryo transfer cycle to achieve a healthy pregnancy. The embryos with chromosomal abnormalities are discarded.