Genetic testing can also be utilized for patients who are at risk for producing embryos that carry improper numbers of chromosomes (aneuploids).
Normally, an individual has two copies of each of 22 chromosomes plus two sex chromosomes (either XX or XY). In some cases, there are either too few or too many copies of specific chromosomes.
The consequences of having an abnormal number of chromosomes vary depending on which chromosome it is. For example, Down’s Syndrome is the result of having an extra chromosome number 21. Turner’s Syndrome is the result of having one X chromosome and no other sex chromosome. The duplication or absence of other chromosomes or multiple chromosomes can result in the death of the fetus and miscarriage later in an established pregnancy, or even failure for the embryo to implant.
This genetic testing is called Preimplantation Genetic Screening or PGS.
Patients who may benefit from this procedure include those who have recurrent IVF miscarriages, repeated implantation failures and patients of advanced maternal age. Ovation Fertility Austin collaborates with several laboratories for PGS testing. Traditionally, laboratories have only screened for the chromosomes that are most commonly seen to be aneuploid. Using colored fluorescent probes designed to attach to specific chromosomes, the laboratory can determine how many copies of each tagged chromosome are present in a cell.
This technique is called FISH (Fluorescent In Situ Hybridization). Each probe lights up a different color, thereby allowing several chromosomes to be visualized at one time. A normal cell should show 2 FISH signals for each of the chromosomes one through 22 and either an XX or XY for the sex chromosomes. Most labs that use FISH test for 5 to 11 chromosome pairs. Ovation Fertility Austin is now working with a laboratory that uses a different technique using DNA markers to tests for all 23 chromosome pairs.
This exciting new test also uses data from the parental chromosomes to enhance the test results from the embryos, thereby making them more accurate. The parental testing is done prior to the beginning of the patients’ IVF cycle. This parental support is also used to determine whether the sperm or the egg contributed to the aneuploidy. Whichever method is used for PGS, as with PGD, one cell is removed from each embryo on day 3 of development and the test results are received by day 5 in time to transfer the embryos with a normal chromosome complement to the patient’s uterus.