Preimplantation Genetic Testing (PGT), formerly known as preimplantation genetic diagnosis (PGD), is a procedure used during in vitro fertilization (IVF) to screen embryos for genetic disorders before they are implanted into the uterus. PGT helps identify genetic defects or chromosomal abnormalities in embryos created through IVF, allowing for the selection of embryos that are free from specific genetic conditions or abnormalities.
There are different types of PGT, depending on the specific genetic testing involved:
1. PGT-A (Aneuploidy screening): This type of testing screens embryos for chromosomal abnormalities, such as aneuploidy (an abnormal number of chromosomes). Aneuploidy can lead to conditions like Down syndrome. PGT-A aims to select embryos with the correct number of chromosomes for implantation, increasing the chances of a successful pregnancy and reducing the risk of miscarriage.
2. PGT-M (Monogenic disorder testing): PGT-M is used to detect specific genetic mutations that cause monogenic disorders, such as cystic fibrosis or Huntington’s disease. This testing is beneficial for couples who are carriers of genetic diseases and want to avoid passing them on to their children.
3. **PGT-SR (Structural rearrangement testing)**: PGT-SR is used when one or both parents have structural rearrangements in their chromosomes, such as translocations or inversions, which can increase the risk of miscarriage or chromosomal abnormalities in their offspring. PGT-SR helps identify embryos that are unaffected by these structural rearrangements.
The PGT process typically involves the following steps:
1. **IVF Procedure**: Eggs are retrieved from the woman’s ovaries and fertilized with sperm in a laboratory setting, creating embryos.
2. Embryo Biopsy: Typically on day 5 or 6 after fertilization, when the embryos have reached the blastocyst stage, a few cells are removed from each embryo for genetic testing.
3. Genetic Testing: The removed cells undergo genetic analysis to detect any abnormalities or mutations.
4. Embryo Selection: Based on the genetic testing results, only embryos free from the targeted genetic condition or abnormalities are selected for transfer into the woman’s uterus.
5. Embryo Transfer: The selected embryos are transferred into the woman’s uterus, with the hope of achieving a successful pregnancy.
PGT offers several benefits, including reducing the risk of passing genetic diseases to offspring, increasing the chances of successful pregnancy and live birth, and potentially reducing the need for prenatal diagnostic procedures like amniocentesis or chorionic villus sampling (CVS). However, PGT is not without limitations and ethical considerations, and it may not be suitable for all couples undergoing IVF. Additionally, PGT can be expensive and is not always covered by insurance.