PGDlab : For Physicians : What is PGD : Q & A

PGD for gender determination selects embryos of the desired gender. Another technology, unique to Genetics & IVF, uses Microsort® sperm separation (currently in a clinical trial) to increase the likelihood of achieving a pregnancy of the desired gender.

This technique can be used alone or with PGD. Get more information about Microsort®.

When does PGD happen in the IVF cycle?
After embryos are created in the laboratory, they are grown for 3 days. On day 3, the PGD biopsy is done and 1 or 2 cells are removed from the embryo. The genetic material inside these cells is tested for gender. On day 5, the woman returns to Genetics & IVF Institute to discuss her PGD test results. Decisions regarding selection of embryos to transfer into the uterus are made with the advice of the medical team.

Is PGD Safe?
Yes. Data from many years of PGD in animals and approximately 1200 live births in humans indicate that PGD does not lead to an increase in birth defects or chromosomal disorders. PGD is done before the embryo’s genetic material becomes ‘active’. Since it is done so early, the cells inside the embryo are still all identical and each cell is capable of becoming any part of a baby. Removal of a few of the cells of the early embryo does not alter the ability of that embryo to develop into a complete, normal pregnancy.

How do they get the cells out of the embryo?

Embryos created in an IVF cycle are cultured in the laboratory for 3 days. By this time they contain approximately 8 cells. Each embryo at this point is called a blastomere. Embryos with normal development on Day 3 will have one or two cells removed for testing in a procedure called a biopsy. The embryos are placed under a powerful microscope and very tiny glass instruments are guided to make a small cut in the zona pellucida, (a tough outer membrane holding the embryo together). Depending on the health and size of the embryo, one or two cells are taken out. The cut then snaps shut and no cells can ‘fall out’ accidentally.

In order to obtain results of the biopsy, the 1-2 cells removed must contain a nucleus, as the nucleus contains the genetic information necessary for testing. If the cell removed has no nucleus or if the nucleus breaks open as it is being prepared, testing is unable to be performed on that cell. Additionally, since embryos are actively growing and dividing, sometimes the cell taken out contains two nuclei. This could mean the cell is abnormal or is caught in the process of division. Testing of these cells may be difficult to interpret.

How exactly is the PGD test done?
Gender is determined by our sex chromosomes. Get more information about chromosomes and genes. PGD testing is different than most genetic testing, since it is done on only one or two embryonic cells and must be completed within 48 hours to allow embryo transfer by Day 5. Since standard chromosome analysis takes several days, a different method called fluorescence in-situ hybridization (FISH) is performed.

Each chromosome has unique areas of DNA present only on that chromosome. A small DNA probe is used to recognize these unique patterns and fluoresce, or light up, when it attaches to the chromosome. Each probe shines light in a different color, allowing several chromosomes to be tested at the same time. This technique is called FISH.

FISH probes for X and Y are used to determine the gender of each embryo. For laboratory control a FISH probe for a different chromosome is also used, typically chromosome 21. The presence of these chromosomes are viewed simultaneously. A normal cell should show 2 FISH signals (or lights) for the numbered chromosome, and either 2 X signals for a female or 1 X and 1 Y signal for a male.

An example of a FISH test showing one X chromosome (green) and one Y chromosome (aqua) for a male. There are two signals for the control FISH probe for a numerical chromosome (yellow).	An example of a FISH test showing two X chromosomes (green) and no Y chromosomes (aqua) for a female. There are two signals for the control FISH probe for a numerical chromosome (yellow).

How are embryos chosen for transfer?
Embryos that have both a normal test result and appearance should be transferred. Sometimes embryos that have normal genetic tests will have a physical problem that prevents them from growing normally. Sometimes embryos that have abnormal genetic tests will appear to be physically normal. The combination of normal genetics with normal physical appearance gives each embryo the highest chance of becoming a healthy pregnancy.

What physical characteristics are used to determine normal appearance?
Embryologists give a “score” to the embryo based on the uniform size of the different cells, the number of cell fragments present, as well as other criteria reflecting the physical appearance of the embryo. Embryos that do not have at least 5 cells on day 3 or embryos that are given a poor score rarely go on to successfully implant.

What if all the healthy embryos are not used?
All decisions about which embryos to transfer and how to use the remaining embryos will be made together with the couple and their doctor(s).

How do I get more information?

To make an appointment for an initial consultation with one of our reproductive specialists,
please call (800) 654-4363 or (703) 698-7355.

For more information about Genetics & IVF Institute's PGD for aneuploidy,
please call (800) 654-4363 or (703) 698-7355
and ask to speak with the PGD counselor OR email PGD@givf.com.

Please click on another question for more information.

• Is your patient a woman over 35?
• Has your patient experienced several miscarriages?
• Has your patient had a prior pregnancy with a chromosome abnormality?
• Has your patient experienced several failed IVF cycles?
• Has conceiving a pregnancy been difficult for your patient due to a low sperm count?
• Does your patient or patient's partner carry a balanced structural chromosome rearrangement?
• Does your patient have a family history of Huntington disease?
• Does your patient or patient's partner carry a recessive genetic disease such as cystic fibrosis?
• Does your patient or patient's partner carry an X-linked genetic disease such as hemophilia or Duchenne Muscular Dystrophy?
• Does your patient want to balance the gender in your family?

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