PGD, PGS, NGS
Embryo biopsy is the technique applied by the embryologist within an IVF treatment in order to remove one or more cells from the preimplantation embryos. These cells will be then further examined by a genetic/molecular laboratory in order to receive information on the genetic status of the embryos. Briefly, this technique is utilised in order to select the healthy embryos prior to their transfer in to the uterus. Embryos that are carrying genetic disorders or chromosomal aberrations will be excluded from the final selection.
The technique can be applied in different developmental stages of the preimplantation embryos. Until recently, most IVF laboratories performed embryo biopsies on Day 3 of development (6-8 cell stage). Day five biopsy is a newer approach that is gaining a lot of popularity among embryologists since it has a few advantages over the cleavage stage embryo biopsy, such as more cells to work with (more DNA), less mosaicism, no impact on embryo development, and fewer embryos to biopsy per IVF treatment. In most cases a fresh embryo transfer is not possible though. Embryos are vitrified and are transferred to a future frozen embryo transfer. In comparison, cleavage stage biopsy carries but there is an increased risk of mosaicim and possible compromise of the implantation potential of the biopsied embryos.
Here at Pedieos we perform embryo biopsy both on day 3 or day 5 of embryo development. In PGD/S IVF cycles, embryo transfer is either performed on day 4 or 5 of embryo development, if biopsied on day 3, or in a future frozen embryo transfer cycle if biopsy takes place on day 5 (trophectoderm biopsy).
Our clinic provides the opportunity of embryo genetic testing for a wide range of indications.
We perform pre-implantation genetic diagnosis (PGD) which involves preferential transfer of healthy/disease – free embryos into the mother’s uterus. This technology provides an alternative to traditional prenatal diagnosis (PND) which involves genetic testing of an already implanted embryo and the possibility of pregnancy termination: The genetic tests that are employed include
- a) PCR (polymerase chain reaction) – indicated for couples at risk for transmitting a specific genetic disease or abnormality to their offspring (single gene disorder like Thalassemia beta, Tay Sacks, Sickle cell Anemiaetc)
- b) FISH (fluorescent in situ hybridization) – is used in embryos of individuals known to harbor a balanced chromosomal translocation or other structural rearrangement.
We can also perform pre-implantation genetic screening (PGS) which involves detection of chromosomal aneuploidies using the
- a) FISH method (approx. 9 chromosomes can be analyzed including the sex chromosomes),
- b) Comparative genomic hybridization (CGH) in which all the 23 pairs (22, X and Y) of chromosomes are analyzed using micro-array technology.
Who can benefit from PGS:
- women of advanced maternal age
- women with a history of recurrent early pregnancy loss
- couples with repeated IVF failure
- severe male factor infertility
- Couples who want to avoid sex chromosome-linked diseases.
During PGS it is possible to select the sex of the embryos when this is clinically indicated. A detailed referral letter describing the clinical indication is always required before the procedure.
Please contact the Centre in order to receive more information on PGD/PGS cycles.
Next Generation Sequencing is the latest tool for screening the Preimplantation embryos prior transfer. NGS is a very accurate method which implicates whole genome amplification to screen the embryos for aneuploides. The advantage of this method is the ability to check the embryonic genome for more than a single alteration without the need of removing two pieces of trophectoderm cells. With NGS we can test the embryos both for chromosomal alterations (aneuploides) and single gene defects simultaneously.