PGS Testing in a Nutshell


Opinions on Embryo Screening from an Integrative Perspective

By Mary Sabo, L.Ac. DACM

Patients undergoing a cycle of In Vitro Fertilization (IVF) have the option of screening embryos using a process called Preimplantation Genetic Screening.  PGS testing involves analyzing the number of chromosomes in a few cells of an embryo to determine if it contains the correct number of chromosomes (normal or “euploid”) or the wrong number (abnormal or “aneuploid”).  Aneuploid embryos may contain too many chromosomes (trisomy) or too few (monosomy) and when transferred often lead to miscarriage or failed implantation.  Occasionally, an embryo is “mosaic” and has both normal and abnormal cells, which is also not ideal for transfer.  Another version of testing called PGD (Preimplantation Genetic Diagnosis) looks for specific genes in an embryo that may put a baby at risk for severe inherited health issues such as cystic fibrosis or other genetic diseases. 

PGS testing is a way to improve the likelihood that a normal embryo will implant and develop into a healthy baby.  The technology has been around since the 90’s, but has come a long way in the past 5 years.  Initial PGS testing was done on embryos that were 3 days old (when an embryo is a ball of only 6-8 cells).  It required extracting a few cells, so it ran the risk of damaging the embryo and, due to the early stage of development, was not always accurate.  Currently, testing is done when an embryo is a blastocyst (5-6 days old) when there are enough cells for it to start to differentiate into three regions: an outer shell, the eventual placenta (trophectoderm), and the inner mass (which will become the fetus).  The sample is taken from the trophectoderm so damage to the embryo is less likely. 

When and why should you test?

Women of all ages produce abnormal embryos.  While it is more likely that women over the age of 35 will have a higher number of aneuploid (abnormal) embryos in an IVF cycle, women in their 20s still produce a percentage of abnormal embryos each cycle during an IVF.  If you ask 10 different doctors about whether or not to test embryos, you may hear 10 different opinions.  Some clinics advise testing all embryos.  Other clinics advise against testing, especially in younger patients.  Some let the patient choose.  Why?  Cost can be a factor. A batch of biopsied embryos can add thousands to an already expensive IVF process.  There is also some speculation that some embryos that test mosaic  (abnormal and normal cells) might be able to self-correct over time.  While there are a handful of cases that may support this as a possibility, the overwhelming evidence suggests that the newest technology for testing blastocysts called Next Generation is accurate and trustworthy. 

One major benefit of testing embryos is getting a better understanding of a couple’s fertility struggles.  If a batch of embryos tests better than average (50%), it can be assumed problems conceiving are potentially caused by something other than egg quality.  If the embryos test mostly or all abnormal, it can be assumed the cause of infertility is egg quality and using donor eggs or another round of IVF might be recommended.  If a clinic performs more than two transfers with “normal” embryos and there is still lack of implantation or early pregnancy loss, further testing may be needed to check for uterine abnormalities, blood clotting, or immune issues, hidden infections, or endometriosis.  Another benefit of testing embryos is screening to rule out certain genetic diseases.  If either partner is a carrier of a genetic disease, the embryos can be screened for that disease using PGD. 

Screening embryos also results in fewer miscarriages and reduces the occurrence of multiples (twins, triplets). When embryos have been screened, most doctors transfer single embryos resulting in singleton pregnancies. While twins and triplets are appealing to some couples, multiples pregnancies are much more dangerous for both the mother and babies.

PGS testing is recommended for women over 35 and for couples who wish to reduce the risk of miscarriage.  Women under 35 or those who produce a lot of embryos may also want to test to help decide which embryos are ideal to transfer.  While it can add costs to an already expensive process, miscarriages and subsequent transfers are also costly, as well as emotionally difficult and time-consuming.