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Preimplantation Genetic Diagnosis, PGD

We were the first IVF clinic in the greater Seattle area to offer this exciting new service. It is offered to couples at high risk of producing genetically abnormal infants, and older IVF patients whose eggs, and hence embryos, may be genetically abnormal, leading to the failure of implantation or early miscarriage, i.e. repeated IVF failure. The biopsy identifies genetically abnormal embryos in couples that are both carriers of deleterious recessive genetic disorders or in cases where one partner is affected by a serious genetic disease.

PGD is the only reliable method for family balancing / gender selection.

Background

Meiosis is the cell division that occurs in the gonads (ovaries or testicles) resulting in the formation of gametes that have only 23 chromosomes (half the 46 present in other normal human cells). This reduction division of cells is necessary to preserve the normal cellular chromosome count (46) after fusion of both the female and male gametes at fertilization .

Meiosis is a cellular division that occurs in two stages. Events during the first meiotic division include pairing and duplication of the 23 pairs of chromosomes with the extrusion of the first polar body of half the genetic material allowing the secondary oocyte to have only 23 chromosomes.

After fertilization, there is further replication of only the cells and not the chromosomes, with extrusion of further genetic material (second polar body) in order to maintain the chromosome count at 23 in the resulting oocytes.

With the fertilization of the oocyte by a single sperm, replication of the cell begins, forms an embryo and eventually several blastomeres. Successful preimplantation genetic diagnosis (PGD) is performed in two ways:

1. Biopsy of the first and second polar body provides valuable information about the genetic makeup of the oocytes (eggs).
2. Biopsy of one cell of the resulting embryo (Blastomere Biopsy) enables us to learn about the genetic make up of the embryo and enables couples to select only unaffected embryos for transfer at the time of IVF. This ensures that infants are born without the serious genetic disorders that may affect one or both of their parents. In IVF cycles where all the embryos are affected, couples may make an informed choice to forgo the embryo transfer and begin another IVF cycle.

The implementation of this program requires a multidisciplinary approach, and we recommend consultation with our genetic counselors and perinatologist, as the specific genetic abnormality of the couple must be known in order to discuss confirmation of an ongoing unaffected pregnancy by chorionic villus sampling (CVS) or amniocentesis.

Preimplantation Genetic Diagnosis- What is Available?

Aneuploidy testing enables embryos to be checked for extra chromosomes that may have serious consequences in life, or may be incompatible with life.  These include sex chromosome disorders, like Turners Syndrome and Kleinfelters Syndrome. Also included are Trisomy 21 (Down’s Syndrome), Trisomy 20, 22, 8, 13, 14, 15, 16, 17, and 18.

Preimplantation genetic diagnosis allows for the accurate determination of sex and is used in family balancing.

Translocations

Polar body testing and or blastomere biopsy are also used to diagnose aneuploids (extra or missing chromosomes) in eggs or embryos.

A specialized laboratory technique known as fluorescent in situ hybridization (FISH) can prevent the initiation of abnormal pregnancies, which may result in non-implantation or miscarriage and increase the stress and disappointment of repeated IVF failures.

Since many IVF failures in women over 35 years of age are thought to result from chromosomal abnormalities, the ability to select chromosomally normal embryos for transfer affords an excellent opportunity to improve success rates.

Preimplantation genetic diagnosis (PGD) for Single Gene Defects

This technique enables us to test an embryo without damaging it by first removing one cell (blastomere) using a technique known as embryo biopsy. The gene of interest is copied many times using the polymerase chain reaction (PCR) and then genetic probes are used to explore the genetic makeup of the embryo.

One common technique is to genetically sex the embryo, as certain genetic disorders such as hemophilia A and muscular dystrophy are X linked.

Single Gene Defects

Other genetic deficiencies that are amenable to testing by PGD include:

Please call or make an appointment with Dr. Kustin to learn if PGD is a viable option for you.