Gender Selection Via Preimplantation Genetic Diagnosis (PGD) - Frequently Asked Questions

What is PGD?

Preimplantation genetic diagnosis (PGD) is a technique in which embryos are biopsied three days after fertilization.  The single cell that is biopsied from the embryo is then used to determine:

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

What is aneuploidy screening?

Chromosomes are microscopic structures found within the nucleus of cells.  A human normally has 46 chromosomes, or 23 pairs of chromosomes.  An embryo receives 23 chromosomes from the sperm and 23 from the egg.  Chromosomes are made of genes, which contain the information that instructs the cell how to function.  Having extra or missing chromosome(s), a condition called aneuploidy, can result in the failure of an embryo to implant, pregnancy loss, and genetically abnormal pregnancies such as Down Syndrome.  It is impossible to distinguish genetically normal embryos from aneuploid embryos just by looking at them under the microscope.

How is aneuploidy testing done?

After the embryo is grown for three days in the laboratory, a technician can open the surrounding shell and remove a single cell (called a blastomere).  This is called a biopsy.  The cells left behind in the embryo generally continue to grow normally.

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

Under a microscope, the chromosomes (identified by color) are counted and the geneticist can differentiate normal cells from aneuploid cells.  Two days after the embryos were biopsied the geneticist issues a report detailing the chromosome test results for the embryos.  The embryos are then chosen for transfer back into the womb by the afternoon of day five.  At this time, the embryo, if it is still growing in the lab, will have reached a stage of development known as blastocyst.

How does PGD help with gender selection?

Some women/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 women or couples who carry a gender-linked genetic disease.  At the time that "FISH" is being done for aneuploidy screening, the geneticist will also be able to determine the sex of the embryo.

The Palm Beach Center for Reproductive Medicine, in collaboration with Palmetto Fertility Center, can perform family balancing in various circumstances.  The potential benefits vs. risks of PGD should be discussed with us in a face-to-face consultation -- Please contact us if you are interested in discussing this further.

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