The latest hot topic just became hotter! Preimplantation Genetic Screening – or PGS – is one of many advancements within the field of in-vitro fertilization (IVF) and infertility treatment. Also referred to as Comprehensive Chromosome Screening or Preimplantation Genetic Testing for Aneuploidy, PGS is the screening of embryos conceived via IVF to identify those with the proper number of chromosomes and thus the highest likelihood of success. While the media, online communities, and scientific field at large have buzzed about PGS for years, recent press has raised new questions. “Is PGS even worth it? Is PGS helping build families or hindering their growth?”
The answer is: “Yes! PGS is worth it, and is helping build families!” As leaders in the field of reproductive genetic testing, CooperGenomics is at the forefront of PGS. In fact, our lab performed the first PGS test years ago, and we’ve continued to dedicate ourselves to researching its impact and advancing the test to provide even better outcomes. We would like to take this opportunity to answer some complicated questions and provide a fuller picture of PGS.
What is PGS, and how is it performed?
PGS is a genetic screening technique which allows us to identify the chromosome content of IVF embryos. Embryos with a normal number of chromosomes (also called euploid) are more likely to lead to a successful pregnancy and healthy live birth than embryos with an abnormal amount of chromosomal material (also called aneuploid).
PGS is performed by taking a small sample of cells from the trophectoderm of a growing embryo and testing those cells. The trophectoderm goes on to become the placenta and other supporting structures of a pregnancy; the inner cell mass, which develops into the fetus, is left untouched throughout the PGS process.
How does PGS help improve my chances of IVF success?
By identifying the embryos most likely to lead to a healthy live birth, you and your physician can prioritize which embryo to transfer– potentially increasing pregnancy rate, reducing miscarriage rate, and reducing the time to a successful pregnancy.
Are all embryos either ‘normal’ or ‘abnormal’?
In recent years, three distinct categories of PGS results have emerged. In addition to the well-understood euploid/normal (expected number of chromosomes) and aneuploid/abnormal (extra or missing chromosomes), scientists can now use next-generation sequencing (NGS) techniques to routinely identify mosaic embryos. Mosaic embryos contain a mix of both normal and abnormal cells.
Previously used technologies were less-sensitive and could not reliably detect mosaicism, meaning embryos could only be classified as normal or abnormal.
Can mosaic embryos make babies?
Data has shown that mosaic embryos – specifically those with a lower level of mosaicism – can successfully implant and lead to healthy live births; however, they do so at a lower rate than normal embryos, and have a higher probability of miscarriage.
It’s important to note here that the ability to identify mosaicism in embryo samples is new, and embryos identified as mosaic may have been called abnormal by previous technologies. It is very likely that we have, unknowingly, been transferring mosaic embryos for years. An article recently published in New York Magazine questioned the utility of PGS, citing two groups who saw success following transfer of abnormal embryos. However, the 24 embryos transferred from one group were not fully abnormal but were in fact mosaic, and the seven analyzed by another group were analyzed with an older technology that could not differentiate between abnormal and mosaic.
What if I had PGS as part of my IVF treatment years ago? Were my PGS results wrong?
No science is perfect, and as with any medical testing there is the chance for misdiagnosis. For PGS performed on older technology platforms (such as aCGH), the published error rate was 2%. Today’s NGS methodologies have an even lower error rate – our data indicates 0.5%.
All of this sounds very complicated! Do you have evidence to support the use of PGS?
While the recent PGS press highlighted interesting results from one small study, it unfortunately failed to acknowledge or share the number of randomized controlled trials (RCTs – the gold standard of research in medicine) on PGS and their supportive findings.
An analysis published by the CDC in 2016 found decreased miscarriage rates (for patients >35 y.o.) and increased live birth rates (for patients >37 y.o.) with IVF and PGS. A 2017 article in Fertility and Sterility (Rubio et. al.) concluded that PGS was “superior” to controls for clinical outcome at first transfer, decreased miscarriage rates, and shortened time to pregnancy for women >38 y.o. In our own experience, we routinely work with centers who see IVF+PGS success rates of up to 60%.
CooperGenomics has a team of dedicated genetic counselors who can help you and your provider decide if PGS fits in your family planning. The field of genetics continues to evolve, and our team remains committed to supporting you throughout your fertility journey. We are confident in the ability of PGS to assist in selection of the embryo most likely to lead to success, and ultimately contribute to building a healthy family.