What Is PGS?
Preimplantation genetic screening (PGS) is a genetic test that screens the embryo for chromosomal abnormalities. A few cells are extracted from an embryo produced in the IVF lab and are sent to a genetics laboratory for testing. PGS determines if the embryo has the correct number of chromosomes. It also detects translocations, when pieces of a chromosome break off and reattach at the wrong place. PGS can also learn an embryo’s gender. Recent advances in the testing include Next Generation Sequencing (NGS) technology, which is far more accurate than the tests used before 2015.
PGS does not test for specific diseases. Preimplantation genetic diagnosis (PGD) screens for a number of different genetic diseases. It may be used when one or both parents are carriers for a genetic disease or if there is a family history of a genetic disease.
Why Use PGS?
Aneuploidy is a condition when an embryo has more than or fewer than the correct number of chromosomes. Chromosomal abnormalities have been shown to be responsible for nearly 70 percent of all early miscarriages. They are also responsible for Down syndrome and Edwards syndrome.
When women are in their 30s about 30 to 40 percent of their eggs have abnormalities. At age 40 the percentage of eggs with chromosome problems climbs to about 60 percent; it is 90 percent by age 44.
Aneuploidy can happen at any age, but it becomes more common after age 35. If a couple has a history of recurrent miscarriage, IVF with PGS may be recommended by a fertility specialist. PGS may also be a choice when a couple has had failed IVF cycles. An abnormal number of chromosomes or translocations have been found to prevent embryos from implanting in IVF.
Screening the embryos for a normal number and arrangement of chromosomes allows only the better quality embryos to be transferred. Recent research has found that using PGS to test embryos and transferring ones with a normal chromosome count increases IVF success by as much as 23 percent.
If one or both partners are carriers of balanced chromosomal translocations, PGS is often recommended to improve their chances of having a healthy baby. Couples who have unexplained infertility may also be candidates for PGS.
If your reproductive endocrinologist recommends PGS, you will receive genetic counseling both before the test and after the results are received. The genetics counselor will help you be prepared for test results and help you deal with your emotions around any decisions you may have to make.