Preimplantation genetic testing is a procedure whereby several cells are removed from an embryo created by IVF. The cells removed are from the trophectoderm which is the part of the embryo that will form the placenta. The DNA from these cells can be amplified and tested for various genetic conditions. Testing is most commonly performed to screen the embryo for aneuploidy (an abnormal number of chromosomes) and is called “PGTa”. Depending on the age of the woman and other factors we expect that some of the embryos created in the lab will have an abnormal chromosome number and therefore would not be suitable for transfer. Embryos with a normal chromosome number would be eligible for transfer.
Genetic testing can also be performed when one or both parents carry a genetic mutation that could result in a severe or life threatening disease in their offspring. Cells from the embryo can be screened for the mutation of interest and affected embryos not transferred thereby eliminating this risk of passing this disease to the offspring. This is called preimplantation genetic testing for monosomy or “PGTm”. Lastly, couples with recurrent pregnancy loss may have a structural rearrangement in their chromosomes that predisposes to repeated miscarriages. Cells from the embryo can be screened for this structural defect thereby decreasing the risk of miscarriage. This is called preimplantation for structural defects of “PGTs”.
Genetic testing of an embryo requires development to the blastocyst stage which is usually seen on the 5th or 6th day after fertilization. Not all of the eggs that fertilize will make it to the stage where they can be tested. The goal is to have multiple blastocysts available for testing as it is expected some of these embryos will be found to be abnormal. If you decide to do genetic testing for one of the above reasons, your doctor will discuss with you the details of the procedure. Genetic testing is an additional expense that not all insurances will cover, even if you have IVF coverage.