PREIMPLANTATION GENETIC TESTING (PGT)

Couples who are carriers of genetic disorders, including recessive or dominant single gene defects, sex-linked conditions, or chromosome rearrangements, face a reproductive risk: affected pregnancies may result in miscarriage or in the birth of a child with significant phenotypic abnormality, sometimes resulting in early death.

Such couples have the option of undergoing prenatal diagnosis once a pregnancy is established, either by amniocentesis or chorionic villus sampling (CVS), to allow the detection of the genetic disorder in the fetus. However, with these procedures, if a genetic abnormality is detected, parents may face the difficult decision of whether or not to continue the pregnancy.

Preimplantation genetic testing (PGT) has been introduced as a technique complementary to prenatal diagnosis in order to increase the options available for at risk couples. Its intended goal is to significantly reduce a couple’s risk of transmitting a genetic disorder or a chromosomal abnormality by diagnosing such conditions in oocytes or early human embryos that have been cultured in vitro, before a clinical pregnancy has been established. After testing, only embryos diagnosed as unaffected are selected for transfer to the woman’s uterus.

The great advantage of PGT over prenatal diagnosis is that a potential termination of pregnancy is avoided. This gives couples the opportunity to start a pregnancy with the knowledge that their child will be unaffected. Consequently, PGT does not require a decision regarding possible pregnancy termination.