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