What’s the Difference?
If you’re looking into IVF, you may have seen references to PGD and PGS. Both are types of genetic testing performed on cells from embryos in the embryology lab, but they have different purposes and screen for different genetic problems. Many people having fertility treatment will not need to have either of these types of testing done, but in some cases PGS or PGD may help your reproductive endocrinologist find healthy embryos to implant in your uterus during IVF treatment.
What Is PGS and When Is It Used?
Preimplantation genetic screening, or PGS, is a type of genetic screening which determines if the cells in an embryo have the correct number of chromosomes. Humans have 23 pairs of chromosomes. Chromosomal abnormalities such as too many or too few chromosomes are among the most common reasons for failure of embryos to implant and of miscarriage, and are more likely to happen as a woman’s eggs get older. PGS does not test for a specific disease. However, Down syndrome is caused by the presence of an extra chromosome 21 and PGS can detect that.
If you are 35 or older and are having IVF treatment with your own eggs or if you have had recurrent miscarriages, your fertility specialist may recommend PGS to increase the chances of transferring a healthy embryo. PGS really can be a game-changer because it permits the reproductive endocrinologist to transfer only the healthiest embryos, increasing the chances of successful IVF. Five or six embryos are needed for this test, which can be challenging, especially for older women with decreased ovarian reserve. Some women may require more than one IVF cycle to grow enough embryos for testing.
This test is an extra step in the IVF treatment and is performed before an embryo or embryos are transferred. Costs include the cost of the cell biopsy at the embryology lab, usually around $1500, and the cost charged by the genetic testing company, which is usually $1000 to $2000, depending on the number of embryos tested.
What Is PGD and When Is It Used?
Preimplantation genetic diagnosis, or PGD, is another type of genetic screening which detects the presence of genes for specific diseases. This test is important if you or your male partner have a history of genetic diseases in your family and you want to be sure you are not passing it on to a child. In some cases you may be a carrier for a disease without having the disease yourself. PGD tests for:
- Translocations of genes (exchange of chromosomal materials or other structural rearrangements), which can cause birth defects, mental retardation, or miscarriage
- Huntington disease
- Marfan syndrome
- Recessive genetic diseases such as cystic fibrosis or Tay-Sachs disease
- Genetic diseases carried on the X chromosome, such as hemophilia or Duchenne muscular dystrophy
- Gender, which allows you to avoid an X-linked genetic disease (mostly boys have those), or balance your family
- Abnormalities in the number of chromosomes
PGD, like PGS, is an extra step in the IVF treatment and is performed before an embryo or embryos are transferred. PGD is a significantly more complex process than PGS since it examines for individual genes. It costs from $5000 to $6000. Either test has a chance of causing harm to the embryo, so it is important to choose a fertility center with an experienced embryologist and a good track record in performing these tests. Your fertility specialist will work with you to create a personalized plan of treatment, and will recommend to you whether either test is needed or not.