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 PGT to be performed a patient must undergo IVF.
PGT-A 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. PGT-A has revolutionized the field as we now have a powerful tool to select the normal embryos in order to increase implantation and pregnancy rates.
In this procedure the embryos are tested for a specific disease such as:
In this procedure the embryos are tested for structural chromosomal rearrangements (where parts of the chromosomes have been rearranged) normally caused by balanced translocations and inversions. Structural arrangements can increase the risk of implantation failure, miscarriage a chromosomal disorder in the baby.
Some of the patients who would benefit from PGT include:
At Fertility Institute of San Diego, we use the latest cutting-edge modalities in an attempt to provide the best service for our patients. The PGT is comprised of 2 steps:
The first step is the embryo biopsy. We usually perform the embryo biopsy at the blastocyst stage of development (day 5/6 embryo). A laser is used to make an opening in the shell of the embryo and a trophectoderm biopsy is performed in which a few placental cells are removed. This is a very delicate procedure that could damage the embryo.
The second step is the genetic testing. The cells that are removed are sent to our reference cytogenetic lab. The tests typically performed on the biopsied cells are either Polymerase Chain Reaction (PCR) in cases where a single gene is being assessed, for PGT-M or PGT-SR or Next Generation Sequencing (NGS) which uses the latest technological breakthrough in whole genome sequencing to study chromosomes at a level which had not been possible before providing the most comprehensive and accurate screening of all 24 chromosomes. This is performed for PGT-A.
PGT is an intricate process, which requires several weeks of preparation. The 6-step process can be summarized as follows:
It is necessary to undergo an IVF cycle in order to perform PGT. You will undergo controlled ovarian stimulation and egg retrieval. Once the eggs are harvested, Intracytoplasmic sperm injection (ICSI) is performed in an effort to maximize the number of embryos. The embryos are then cultured to the blastocyst stage.
A specialized laser is used to make an opening in the shell of the embryo and a few cells are removed. This is typically performed on a day five embryo or a blastocyst. These cells are sent to the cytogenetic lab.
Immediately following the biopsy, the embryo is cryopreserved or frozen for later transfer once the results are known. One benefit of embryo freezing is that they can remain frozen for years for later use.
Depending on the indication for the PGT either Polymerase Chain Reaction (PCR) or Next Generation Sequencing (NGS) in which all 24 chromosomes are screened will be performed. The results are reported within 7 days.
We welcome the opportunity to answer any questions you may have about your fertility treatment. Here at Fertility Institute of San Diego, you will be treated with compassion and care.