Genetic testing of embryos is a state-of-the-art procedure, which enables us to screen embryos for genetic diseases before the embryos are transferred into the uterus. The purpose of this is to decrease the likelihood of finding chromosomal abnormalities, once the patient is pregnant, during prenatal diagnosis with tests such as chorionic villus sampling, amniocentesis or fetal blood cell testing. In order for PGD to be performed a patient must undergo IVF.
There are 2 types of genetic testing:
Preimplantation Genetic Diagnosis (PGD):
In this procedure the embryos are tested for a specific disease such as:
- Chromosomal translocations (where parts of the chromosomes have been rearranged).
- Single-gene disorders where there is a mutation in a single gene. There are over 4,000 single-gene disorders. The most common diseases tested for are Cystic Fibrosis, Fragile X, Thalassemia, Sickle cell, and Huntington’s disease.
- Inheritable cancers such as BRCA1, which would increase the chance of passing the disease to your child.
- Sex selection for inherited diseases that are sex linked.
Preimplantation Genetic Screening (PGS):
- PGS tests for the overall total number of chromosomes present in the embryo. In this procedure the embryos are screened for aneuploidy, which is testing for missing or additional chromosomes. An example of this would be Down’s syndrome which consists of an extra chromosome 21. As women age, the egg quality decreases and as a result the incidence of chromosomal abnormalities in the eggs increases. Embryos with missing or extra chromosomes generally result in either a miscarriage or a baby with chromosomal abnormalities. In the past, embryo selection for transfer was based on the “look” of the embryo. However we know that this can be misleading as even “good looking” embryos can be aneuploid or abnormal. PGS has revolutionized the field as we now have a powerful tool to select the normal embryos in order to increase implantation and pregnancy rates.