What is Preimplantation Genetic Testing?
Preimplantation genetic testing is available to anyone undergoing in vitro fertilization (IVF). IVF involves stimulation of the ovaries to release eggs, followed by fertilization of those eggs with a partner’s or donor’s sperm sample. The resulting embryos are allowed to grow inside a carefully controlled incubator for several days. It is at this point that the fertility lab can take a small sample of the embryo for testing.
Day 3 or “blastomere” biopsies occur on the third day following conception, and involve removing a single cell from an 8-10 cell embryo.
Day 5/6 or “trophectoderm” biopsies occur on the fifth or sixth day following conception, and involve removing approximately 5-10 cells from the outer layer of cells (the trophectoderm) from a 100-200 cell embryo.
(For information regarding what type of biopsy is right for your situation, please consult your fertility specialist.)
If a couple wishes to have preimplantation genetic testing, the embryo biopsy sample is sent to a laboratory specializing in this testing. Preimplantation genetic testing can be further broken down by category:
Also referred to as comprehensive chromosomal screening, PGS evaluates the embryo’s chromosomes for abnormalities involving the wrong number of chromosomes (aneuploidy), or large (>30 Mb) regions of chromosomal gains or losses. Since the chromosomes carry the instructions for normal growth and development, changes to the amount of this information can cause problems, including failed implantation of the embryo, miscarriage, or the birth of a child with developmental and/or physical abnormalities. By transferring chromosomally normal embryos, a couple can improve their chances for a healthy pregnancy.
Individuals who are at an increased risk of having a child with a specific single gene disorder or a specific chromosomal abnormality due to their own genetic status can undergo PGD to determine whether or not the embryo is affected with the specific disorder of concern. As part of this process, the embryos are also evaluated for whole chromosome and large segmental (>30 Mb) aneuploidy.