Genetic Testing – Preimplantation Genetic Diagnosis (PGD)
Also known as Preimplantation Genetic Screening (PGS), the purpose of this test is to evaluate the chromosomal makeup of an egg/embryo. Because the majority of miscarriages are due to chromosomal abnormalities, many couples undergo Preimplantation Genetic Diagnosis in order to select embryos that are chromosomally “normal” and increase their chances of IVF success. An egg/embryo with too many or too few chromosomes will either fall under the following:
- Fail to implant in the uterus
- Lead to a miscarriage
- Result in a chromosomal birth defect such as Down Syndrome or Turner Syndrome
Preimplantation Genetic Diagnosis (PGD) Gender Selection
Another reason for performing PGS is for family balancing through gender selection. Because the gender chromosomes are identified during the test, it is possible to select a “male” or “female” embryo for transfer to the uterus. After the egg is fertilized and progresses to the embryo stage, one or more cells are removed from each embryo to be tested.
Should I have genetic testing/PGD done on my embryos?
This depends on a number of factors including your age, medical history, and other risk factors. In women above the age of 35, genetic testing can improve pregnancy rates by identifying those embryos that are most likely to make a baby. The additional cost may negate the advantages for some couples. IT IS IMPORTANT TO UNDERSTAND THAT THE TESTED CELLS MAY NOT BE REPRESENTATIVE OF THE WHOLE EMBRYO. There is a 10% false positive and 10% false negative rate. For example, at age 40, the risk of Down’s syndrome is around 1%. Because the test is only 90% accurate, the risk of Down’s would be 1/1000. Testing every cell in an embryo would damage it and limit the usefulness of such a test. Also, as the graph indicate, even when tested the live birth rate is still around 50%.