PGT – Genetic Testing of Embryos

Gain peace of mind with PGT

Our current technology for determining the genetic makeup of embryos prior to transferring them has never been better. We are now able to remove 5-10 cells from a five day old embryo (blastocyst). We can have the complete chromosomal composition of it back in time for transferring it fresh the next day. This is a tremendous advantage for our patients who would like to improve their chances of getting pregnant by transferring back only the best embryos. Patients can choose from two types of preimplantation genetic testing, or PGT.

Preimplantation genetic testing (PGT-A)

The first type of genetic testing gives us information about the number of chromosomes in each embryo. This is PGT-A. It is useful for women who are at risk for having eggs that are chromosomally abnormal. We know that as women age the percentage of chromosome abnormality goes up significantly. From our experience, at age 35 the incidence of genetic abnormality is about 75% of all eggs. At age 40 this percentage is 90%, and by age 45 it is practically 100%. For this reason it is helpful to know which embryos have normal chromosomes and which do not. It is not possible to tell a normal embryo from an abnormal one simply by the way it looks under the microscope.

A normal embryo has 46 chromosomes, 22 pairs of autosomes and one pair of sex chromosomes. Our PGT-A method involves removing 5-10 cells from a five day old embryo that has hundreds of cells. We send these cells to a special laboratory. Tehy can tell us how many chromosomes each embryo has and which ones are are abnormal. We get this information within 24 hours which allows us to transfer the normal embryos back without having to freeze them. Since we know about all 46 chromosomes, we also know the gender of each embryo. As such, couples can select the gender of the embryos they want to transfer. This technique has improved the pregnancy rates of IVF and allows us to freeze fewer embryos as well.

Pre-Implantation genetic testing (PGT-M)

The second type of genetic testing allows us to determine if an embryo is carrying a gene mutation that could cause a specific disease. There are currently hundreds of diseases that can be diagnosed this way. Genes are small pieces of DNA that are present within a single chromosome. If they are abnormal in some way they can lead to a child with a particular disease such as cystic fibrosis for example. If the parents are known to be carriers of such a disease, they could therefore pass on this disease to their future offspring. When doing this type of testing we must first characterize the particular gene mutation in question. Once this is done, a probe is designed which is a laboratory tool used to look for the mutation in the cells obtained from the embryos from the prospective parents.

The embryo biopsy is performed in the same way as PGT-A but instead of testing for the chromosomes the laboratory looks for the specific gene mutation instead. We are then able to determine which embryos would lead to children with the disease, which ones would be normal and which ones would be carriers of the mutation but would not have the disease. The parents could then choose which embryos to transfer and which ones to freeze. We are also able to determine the chromosome makeup of each embryo at the same time, however this requires that we freeze all of the embryos and transfer them at a later date.

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