Preimplantation Genetic Diagnosis (PGD)


What is PGD?


Preimplantation genetic diagnosis (PGD) is a diagnostic test for detection of chromosomal (genetic) abnormalities in the embryo during In Vitro Fertilization  (IVF) therapy.


How is PGD done?

PGD involves removal of one or two cells (blastomeres) from an early 6-8 cell stage embryo and the use of sophisticated laboratory tests to check the embryonic cells for various genetic abnormalities. Only those embryos which are found to be normal are then transferred into the uterus, while the abnormal ones are discarded.

Current genetic techniques in PGD include:

 
Karyotype – The embryonic cells are tested for extra, missing or abnormal chromosome segments which can cause a problem for the developing embryo.
 

FISH (Fluorescence in situ hybridization) analysis - This technique utilizes labeled or fluorescent probes to identify specific chromosomes (such as the X, Y, 13, 18, 21) in a single cell removed from a 6-8 cell stage embryo. This technique can help determine the sex of the embryo and to look for extra or missing chromosomes or to identify specific pieces of genes in the embryonic cell. Pieces of chromosomes that have similar structure to the probe will be tagged and seen with a special microscope.


PCR – is a technique to detect a mutation in a single gene such as cystic fibrosis.


Is PGD for me?


The test has limited usefulness because of the high-cost of the procedure, technical difficulties in performing the procedure and diagnostic limitations. PGD is indicated in patients with abnormal chromosomes or genetic abnormalities, such as (cystic fibrosis), as a way to prevent transmitting the abnormal gene to their children.


What is PGS?


Routine genetic screening of all embryos to select only the normal ones during IVF is called Preimplantation Genetic Screening (PGS).


Why not routinely screen all embryos for genetic abnormalities?


To date, PGS has not been shown to be helpful for patients with repeated IVF failures, older patients   or patients with recurrent miscarriages. In fact, some marginal embryos may survive implantation into the uterus but may be vulnerable to damage from embryo biopsy. This means that women with poor quality embryos have a significantly lower probability of pregnancy if their embryos are biopsied.

PGS is associated with 15-20% false positive results. This means that 15-20% of normal embryos may be misread as abnormal, making them unsuitable for transfer into the woman’s uterus. Another problem with PGS is that there is a 5% false-negative results (undetected abnormal embryos), necessitating amniocentesis later in pregnancy to make sure that the embryo is completely normal.

The Practice Committees of SART and ASRM published an assessment of PGD/PGS. It concluded that available evidence does not support the use of PGS, as currently performed, to improve live-birth rates in patients with advanced maternal age, with previous implantation failure and patients with recurrent pregnancy loss. BocaFertility’s policy is to offer PGD to those patients at risk of transmitting a chromosomal abnormality or single gene defect such as cystic fibrosis and for couples seeking non medical gender (sex) selection since the PGD results also include information on the gender of the embryos.


To learn more about PGD at BocaFertility give us a call at (561) 368-5500.

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