Preimplantation Genetic Testing (PGD/PGS)

It is the process of removing a cell from an embryo (formed by IVF) for genetic tests prior to transferring it into the uterus .

blastomere-biopsyPreimplantation genetic diagnosis is used to diagnose a specific genetic condition before transferring to the uterus .

Preimplantation genetic screening is used to test overall chromosomal normalcy in embryos .

Some  of the disorders can be screened and diagnosed such as translocations or inversions .

It is especially indicated in cases where

  • age of the wife is >35 years
  • history of prior pregnancy with chromosomal anomaly
  • Balanced structural rearrangement in any of the partners
  • Autosomal dominant genetic disease in any of the partners
  • History of multiple implantation failures
  • History of recurrent abortions

The different stages of egg and embryo which can be biopsied are :

1)Polar body biopsy – A mature egg has one polar body and after fertilization has 2 polar bodies . Biopsy of polar body does not involve taking any material from the embryo but there is still a chance to hamper the developmental potential of the embryo post biopsy .

2)Cleavage stage biopsy on Day 3 –In this procedure 1-2 cells are removed from the embryo after removing a part of zona pellucida . This can also be detrimental to embryo development . The results of the tests can be obtained in 48 hrs and a fresh embryo transfer of normal embryo can be carried out .

3)Trophectoderm biopsy is performed at blastocyst stage on Day 5 .The resulting embryo is frozen and after the results are ascertained the normal embryos can be transferred in subsequent frozen embryo transfer cycle .

Various methods used for genetic analysis :-

  • Fluoresecent In Situ Hybridization (FISH)
  • Array Comparative Genomic Hybridization (aCGH)
  • Single nucleotide polymorphism microarrays (SNP)
  • Quantitative real time polymerase chain reaction(qPCR)