Preimplantation genetic testing encompasses types of testing that can be performed in the early stages of embryo development with the intent of identifying the healthiest embryos.
Preimplantation genetic diagnosis (PGD) is used by parents-to-be who have a personal or family history of a known genetic condition that they wish not to pass down to a child. Many diseases, such as cystic fibrosis, sickle cell anemia, Hemophilia, Tay-Sachs disease, Fragile X syndrome, among many others, are associated with known genetic mutations that, through PGD testing, can be identified in an embryo, thereby implanting only the embryos without the mutation and minimizing the chances of having a child with that specific disease. PGD can also be used for parents carrying a gene associated with certain cancers such as Breast, Ovarian and Colon.
Preimplantation genetic screening (PGS) looks for abnormalities caused by too many or too few chromosomes in the embryo’s DNA. If an embryo has too many or too few chromosomes, the chances of pregnancy are lower, while the chances of miscarriage are significantly higher, as are the chances of live births with diseases such as Down syndrome or Edwards syndrome.
Both types of genetic testing require that cells be removed from the embryo, also known as embryo biopsy. The embryo is then frozen and the biopsy specimen is sent to a reference lab which will analyze the DNA from the biopsy specimen. Within a short time, a report will be issued regarding each embryo and its genetic quality. Based on this information, in a frozen embryo transfer cycle, we can confidently implant the healthiest embryo.
It is important to understand that many syndromes and anomalies in children and adults are not genetically linked and, therefore, cannot be screened for.
Benefits of using pre-implantation genetic screening in conjunction with IVF
In traditional IVF, embryos are selected for transfer based on their morphology, or what they “look” like. Each embryo is given a grade based on expansion and organization of cells, with the thinking that the embryos with the highest grades are those with the best quality. Research shows, however, that it is possible to have embryos with high grades that have the wrong number of chromosomes and therefore will either not achieve a pregnancy or lead to a miscarriage.
Such abnormalities are common. In women age 30 and under, 30 to 40 percent of embryos that develop to day 5 and 6 blastocysts exhibit chromosomal irregularities. That percentage increases to 70 to 90 percent in women over age 40.
Considering the regularity of chromosomal abnormalities, testing allows for the selection of embryos that have the greatest chance of creating a healthy pregnancy. For this reason, transfer of only chromosomally healthy embryos doubles the probability of implantation compared to embryos that were not genetically tested. In short, you are more likely to become pregnant from tested embryos than untested embryos.
In addition, genetic screening reduces the chance of twins or higher order pregnancies—because each tested embryo has a higher chance of developing into a fetus, fewer embryos can be transferred. We often recommend transferring only one embryo, which reduces the chance of multiples to under 2 percent.
The use of tested embryos also decreases the risk of miscarriage and pregnancy loss, especially in women who are older, have experienced recurrent miscarriage, or are at an increased risk for chromosomal abnormalities called translocations.
Through our clinical relationship with Yale Medicine, we are able to offer the most cutting edge technology, allowing us to offer our patients the greatest chances of achieving their dream of a healthy baby.