PGD (Preimplantation Genetic Diagnosis) and Family Balancing

Thanks to a technique called FISH (fluorescence in-situ hybridization), embryos can be tested for aneuploidy (extra or missing chromosomes), gender, or a specific genetic mutation before they are implanted. Such testing is helpful for couples who have had trouble maintaining a successful pregnancy, who may carry the gene for a disorder such as Tay-Sachs, or who wish to determine the gender of am embryo prior to implantation because they have a gender imbalance among their current children.

At Palmetto Fertility Center in Miami and Miramar, Florida, Dr. Michael Graubert is proud to offer these services to qualifying couples.

• PGD (Preimplantation Genetic Diagnosis)
• Family Balancing

PGD (Preimplantation Genetic Diagnosis)

Preimplantation genetic diagnosis is a technique in which human embryos are biopsied at the eight-cell stage (day three after fertilization). The single cell that is biopsied from the embryo is then used to determine:

• whether the embryo itself has an abnormal number of chromosomes (aneuploidy screening);
• the sex of the embryo;
• whether the embryo may be carrying a genetic disease that either one of the parents may carry (single gene deletion testing).

Aneuploidy Screening

Chromosomes are structures found in the center (nucleus) of cells. A human typically has 46 chromosomes, or 23 chromosome pairs. An embryo receives 23 chromosomes from the sperm (father) and 23 from the egg (mother). Chromosomes are made of genes, which contain the information that instructs the body how to function. Having extra or missing chromosome(s), a condition called aneuploidy, can result in lack of implantation of an embryo, pregnancy loss, and other conditions such as infertility and Down syndrome. It is impossible to distinguish genetically normal embryos from embryos that have an abnormal number of chromosomes (aneuploidy) just by looking at them under the microscope. This is why genetic testing can be useful for certain patients.

Who can benefit from PGD for aneuploidy?

PGD to detect aneuploidy is offered to patients undergoing in vitro fertilization (IVF) who are 35 years old or older. It may also be used for patients of any age who have failed to conceive despite several IVF cycles. Other patients who may benefit are women with a history of miscarriages, especially when testing reveals no clear explanation. Patients who have had an aneuploid pregnancy in the past may also want to consider PGD for aneuploidy.

How is the test performed?

When the embryo reaches the eight-cell stage, a technician can open the shell around it and remove a single cell (blastomere), then perform a biopsy on the cell. The cells remaining in the embryo will continue to grow normally.

The biopsied blastomere cell is fixed to a glass slide and analyzed by an outside reference laboratory using a technique called fluorescence in-situ hybridization, or FISH. This technique uses probes — small pieces of DNA that are a match for the chromosomes to be analyzed — to count the chromosomes. These probes are attached to molecules that act as colorful markers. The probes are applied to the biopsied cell and attach to the chromosomes.

Under a microscope, the chromosomes, identified by color, are counted, and the geneticist can differentiate normal cells from cells with aneuploidy. The geneticist then issues a report by the morning of day five detailing the chromosome test results of the embryos. The embryos will then be chosen for transfer back into the womb by the afternoon of day five. At this time, the embryo will be a blastocyst.

Family Balancing

Using the FISH technique for aneuploidy screening will also disclose the sex of the embryo. Most couples undergoing IVF will not choose an embryo for replacement based on the sex of the embryo. However, some couples wish to undergo IVF to determine the sex of the embryo if, for example, they have two girls, and wish to have a boy. Another indication for determining the sex of the embryo before embryo transfer is for couples who may be carrying a gender-linked genetic disease.

Palmetto Fertility Center will perform family balancing in certain circumstances. Please contact us to find out more.

Single Gene Testing

Sometimes a potential parent, or both parents, may be carrying a genetic mutation for a certain genetic disease (Tay-Sachs disease, for example). In this situation, it is useful to know whether an embryo is carrying a genetic mutation before it is placed in the womb. The embryo is tested via a biopsy, and the DNA of the embryo is analyzed for genetic disease. This way, a couple carrying a genetic disease can have a child that is not affected by the disease.

PGD and Family Balancing at Palmetto Fertility Center

Preimplantation genetic diagnosis and family balancing are relatively recent innovations that help couples create healthy, happy families. If you live in South Florida and interested in either of these techniques, contact Dr. Michael D. Graubert today to learn more.

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