What is Preimplantation Genetic Testing?
Preimplantation genetic testing is a screening test used to determine if genetic or chromosomal disorders are present in embryos produced through in vitro fertilization (IVF).
Why Should you Consider Preimplantation Genetic Testing?
Well over half of IVF treatments are unsuccessful because the embryo(s) transferred have the abnormal total number and/or distribution of chromosomes called aneuploidy. Ideally, we test embryos for abnormalities and then transfer a single embryo with the normal number and distribution of chromosomes called euploidy. By doing so, there is a better chance of becoming pregnant, avoiding a miscarriage and having a healthy baby. The precision of selecting a single euploid embryo to transfer would serve to ease concerns related to multiple gestation (ex: twins), ovarian hyperstimulation syndrome early in pregnancy, etc.
Preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) are types of testing that can be performed on an embryo in the early stages of development.
What are PGD and PGS?
Preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) are types of testing that can be performed on an embryo.
Humans have 46 chromosomes, and there can be thousands of genes within a single chromosome. PGD targets the presence of a mutation in a single gene that causes a disease. As this type of test identifies a specific disease, we use the term ‘diagnosis’ and thus preimplantation genetic ‘diagnosis’.
PGS testing surveys the entire length of each chromosome. PGS searches for random abnormalities. This is a general test rather than one looking for a specific abnormality. For this reason, we use the term preimplantation genetic ‘screening’. Abnormalities can involve duplications, deletions, rearrangements of parts of a chromosome or the entire chromosome. 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. The abnormality percentage increases to 70 to 90 percent in women over age 40.
Genetic technologies are rapidly evolving to simultaneously perform PGD and PGS in the same analysis. It would be nice to know your child likely won’t have the single gene mutation causing cystic fibrosis by using PGD or have an extra 21st chromosome called Downs Syndrome by using PGS. Unfortunately, no single technology provides us with all we would like to know. For now, final genetic testing results are reported as estimates of reduced risk rather than absolutely free of risk. Everyone hopes to have a perfect baby, but genetic testing is still not a guarantee. Even so, PGD and PGS are still the best options to help choose the best embryo to transfer.
Preconception Screening is an Essential Step to Learn if You Should Consider PGD
Preimplantation genetic diagnosis (PGD) is most often used by couples struggling with issues related to a known family or personal history of a specific abnormality in a single gene contained within the much larger chromosome of every cell in the body. For example, once the genetic disease is discovered in an affected family member, such as a first born son with Fragile-X syndrome, the parents will seek medical care to prevent having a second child with the same genetic disorder that leads to a lifetime of severe physical and cognitive disability. Genetic mutations cause diseases such as the ethnicity related group of diseases within the Ashkenazi Jewish members of our community, the hemoglobin abnormalities sometimes found in people with ancestry from Africa, the Mediterranean Sea and Pacific Ocean shores of the world or those independent of ethnicity, such as cystic fibrosis, spinal muscular atrophy (SMA) and fragile-X. Children born with these genetic diseases may fail to survive beyond birth or the first few years of life or could suffer greatly into adolescence and adulthood. PGD helps to avoid having a child with these genetic diseases.
Testing both parents to learn if either or both are carriers (unaffected or mildly affected by the mutation) of the genetic mutation can be performed prior to trying to conceive. Genetic counseling is a key step in considering PGD and setting realistic expectations for benefits and risks. If there is significant risk of having an affected child or for miscarriage if an embryo is affected by the mutation, then the couple can undergo in vitro fertilization (IVF) therapy. Embryos that grow to a blastocyst can undergo a biopsy. Some cells are removed from the embryo without harming it. The cells undergo genetic testing. If the test results are favorable, then an embryo is suitable for transfer into the uterus.
Be Cautious About the Marketing Hype of PGS
There are websites that tout very high success rates with PGS, but the devil is in the details. Here’s an example of common marketing tactics. The webpage may claim a 70% ‘success’ rate for IVF with PGS in brightly colored graph form. In fine print, there is a description that the data is limited to women who had an embryo transferred. At first glance, it looks like this clinic has great success using IVF with PGS. In reality, 100 couples may have had IVF with intention for PGS, and 50 couples had PGS results with at least one normal embryo. For the remaining 50 couples, none of the embryos had a normal PGS result or they had no embryo with advanced development upon which to perform PGS. Therefore 50 couples did not have an embryo to transfer. Among the 50 couples with at least one PGS normal embryo, 35 become pregnant. The clinic displays a graph showing 70% ( 35 of 50) success for couples undergoing PGS (with an embryo transfer written in fine print). The 50 couples who had no normal embryo and no transfer were not included in the graph. It turns out that for all couples intending to have a baby with PGS to assist, only 35% (35 of 100) became pregnant.
What if PGS or PGD Doesn’t Result in a Pregnancy?
There is good hope to have a healthy child with preimplantation genetic testing. Even so, it’s important to know that planning to have PGS or PGD is no guarantee the embryos can be tested or, if tested, that there will be a normal result. If the PGS or PGD process brings bad news—such as embryos that don’t grow or results that show all embryos are genetically abnormal, at least there is discovery as to why IVF was not successful.
When things don’t work as hoped, the sense of loss and grief can be intense. Persistence is a powerful attribute to have and apply in this situation. Our Michigan Reproductive Medicine (MRM) team is here to support you every step of the way, cheering your success and supporting you through challenging and frustrating times. Our infertility support group led by former patients of our practice provides an amazing, organically patient-centered experience to all that participate.
Questions About PGS and PGD? Call MRM and Come In for a Consultation!
If you are considering in vitro fertilization and PGS or PGD and want to know if this treatment may be right for you, meet with one of our physicians at MRM for a consultation.
Call us at (248) 593-6990 or click here to contact us. You are also more than welcome to come visit our fertility center so you can see our facilities for yourself!