IVF technology revolutionized the field of reproductive medicine and helped millions around the world struggling with infertility become parents. More than 400,000 babies from 1.6 million ART cycles are born around the world every year. To date, it is reported that over 8 million babies were born through IVF.
However, IVF success depends greatly on the quality of the embryo. So far, the embryologists had to rely solely on morphology to choose a healthy embryo with the most chances to end up in a live birth. However, Embryos that look good under the microscope don’t always have what it takes to produce a viable pregnancy. Chromosomal Aneuploidy in embryos, embryos with an abnormal number of chromosomes will fail to develop normally and in most cases will result in spontaneous miscarriages. Aneuploidy cannot be detected by a microscope and requires genetic testing.
Genetic testing on live embryos was a challenge for many years. However, with scientific and technological advancements, the concept of genetic testing of embryos was first successfully performed in 1989 when scientists reported the screening for Y chromosome in embryos to reduce the chances of X-linked recessive disease. The technology further developed and now Preimplantation Genetic Testing (PGT) is available in many fertility clinics as an additional screening tool that allows embryologist to select the embryo with the most chances to implant and result in a viable pregnancy.
PGS (also known as PGT-A) is a highly specialized genetic testing for screening chromosomal abnormalities in embryos. On day five or six after fertilization, the embryologist will remove a few cells from the developing embryo that will be used to verify the presence of all 23 chromosomes. The cells are taken from the part of the embryo that will later form the placenta. The results will allow selection of embryo/s with a normal number of chromosomes. These embryos are more likely to result in an ongoing pregnancy with a lower risk of miscarriages. The process of PGS is illustrated in this great animated video.
Historically, this test was performed on day 3 when the embryo has just eight cells. These methods were not sensitive enough and prone to misdiagnosis. In addition, these test only identify aneuploidy in up to 12 chromosomes. With scientific advancements, PGS is now available to simultaneously evaluate the ploidy status of all 23 chromosomes pairs. Further developments allowed embryologists to perform the biopsy in blastocyst stage (day 5-6 after fertilization) and on the extra-embryonic (Trophectoderm) tissue, which increased accuracy and reduced the risks for the embryo development.
PGS is a powerful new tool in the optimization of assisted reproductive technologies. Studies show PGS improve IVF results by increasing pregnancy and birth rates and decreasing miscarriage rates. There are several methods available for PGS. All genetic technologies will equally identify “whole chromosome” aneuploidy. However, some genetic technologies are more sensitive and will identify large segmental chromosome duplications or deletions.
Over the years several methods were developed to define the number of copies of each of the chromosomes. These methods differ in the mechanism that reports on the presence of a chromosome and the extent that each of the chromosomes is covered by the reporting mechanism. These methods include:
It is important to note that while the accuracy of these tests improved significantly over the years, prenatal genetic testing is still recommended once clinical pregnancy is achieved.
The fertility specialist may recommend additional PGS testing, but it is an elective test. It’s the parent’s choice to include it or not. While this looks like an additional upfront expense, it might save you time and money down the road by avoiding embryo transfers that have no chance to implant.
Do you have more questions about PGS, our team of experts is here for you! Call us to learn more about your options.