We are one of the most experienced clinics in the Pacific Northwest with regard to preimplantation genetic testing, an umbrella term that refers to both Preimplantation Genetic Diagnosis (PGD), and Preimplantation Genetic Screening (PGS). We have been carrying out embryo biopsies since 2003, allowing parents more choices than they were previously allowed in their reproductive health.
With our state of the art laboratory and fully trained staff our clinic is a great choice if you require PGD/PGS testing for any reason. We constantly evaluate and then incorporate new technologies as appropriate.
What is PGD/PGS used for?
Currently, PGD/PGS can be used for four different types of abnormalities:
- Single gene defects which cause disorders such as Cystic Fibrosis or Huntington’s disease
- Numerical chromosomal abnormalities (aneuploidy) which cause disorders such as Down syndrome (an extra chromosome 21) or Turner’s syndrome (females with one X-chromosome instead of two)
- Structural chromosomal abnormalities such as various forms of translocations, which increase miscarriage rates
- Gender selection / family balancing
Who may want to use PGD/PGS?
PGD can be used by both fertile and infertile couples. Couples who are carriers of a familial single gene disorder may wish to access PGD to have children without the particular genetic disorder. PGS for aneuploidy screening is useful for couples who have suffered from repeated miscarriages. Furthermore, based on the most recent data it is recommended for all patients undergoing IVF.
Learn More About Pre-implantation Genetic Diagnosis (PGD)
Each cell of the body contains structures called chromosomes within their centers or nuclei. A human cell typically contains 46 individual chromosomes, grouped as 23 pairs. The embryo will get 23 chromosomes from the sperm and the other 23 from the egg. These chromosomes are made up of genes, which are the blueprint that contains instructions as to how the cells within the body should function. It is very important, therefore that each cell contain a full complement of 23 pairs of chromosomes, as any imbalance in the number of chromosomal pairs (aneuploidy) can give rise to a failure of the embryo to implant, cause early pregnancy loss, or other conditions, such as Down’s syndrome. By analyzing the chromosomal content of pre-implantation embryos it is possible to determine which embryos are more likely to implant and create a normal ongoing pregnancy. Currently there are two options for preimplantation genetic testing.
Preimplantation Genetic Diagnosis (PGD) is a procedure used in conjunction with in vitro fertilization (IVF) to test early human embryos for serious inherited genetic conditions and chromosomal abnormalities before they are transferred to a woman’s uterus. PGD was first carried out in 1989 and has evolved significantly since. PGD now refers to testing the embryos for a specific genetic condition such as cystic fibrosis or hemophilia. The procedure is sought by both fertile and infertile couples at high risk of having children with a serious genetic condition. With preconception screening such as the panels available from Counsyl or Natera, we can readily identify couples that are at increased risk for any of several hundred diseases before pregnancy! It can also be used as a screening procedure to determine if an embryo is chromosomally normal prior to transfer. Before PGD the only testing option available to couples at risk of passing on a genetic disorder to their child was prenatal diagnosis. PGD offers another choice to carriers of serious genetic disorders and involves making decisions about the future of an affected embryo, rather than an affected pregnancy. PGD can be used to test for essentially any disorder that could be detected by amniocentesis – the list now numbers in the hundreds.
In the case of testing for a genetic condition, a marker specific to the condition and the couple is developed prior to testing. This can then be used to specifically pinpoint any embryo that contains the gene disorder in question. In the case of a recessive condition, 2 copies of the gene disorder are required to exhibit the disease, and if only 1 is present then the embryo is considered to be a “carrier”. With dominant conditions, the presence of just 1 copy will cause the disease to be exhibited. A full genetic consultation is always recommended prior to undergoing PGD.
Preimplantation Genetic Screening (PGS) is a more recent term that refers to screening embryos to make sure they have both the correct number of chromosomes, and that each chromosome does not have any structural abnormalities. This process is often referred to as anueploidy screening. PGS looks at the general composition of the chromosomes and is what is recommended for all IVF patients.
PGD/PGS involves several steps:
- The creation of an embryo via IVF (using ICSI for single gene disorders)
- The removal of a small group of trophectoderm (future placental) cells each appropriate day 5 / 6 blastocyst
- The genetic testing of these cells for a specific genetic condition (PGD), + anueploidy screening (PGS), or just anueploidy screening (PGS)
- The subsequent transfer of unaffected embryo to a woman’s uterus
After removing a small section of the trophectoderm from the embryo, the cell mass is frozen in transport media before being shipped to a reference laboratory for analysis. The embryo itself is then frozen and stays in our laboratory. This will then give us a picture of the chromosomal content of the embryo. In conjunction with the embryo score, we have the ability to predict more easily which embryo should be transferred.
What are the potential benefits of PGD/PGS?
It allows for the selection of embryos with a normal chromosomal content.
PGD offers people at high risk of transmitting a serious genetic condition to their children an alternative to their existing options of:
- Avoiding conception
- Attempted natural conception, involving a known risk to the health of the future child
- Attempted natural conception, and pregnancy termination if the fetus is found to be affected by the condition following prenatal diagnosis
- Using donated gametes or embryos in an attempt to conceive an unaffected child
For many people, termination following prenatal diagnosis is either unacceptable or less preferable because of:
- Ethical concerns based on beliefs about the moral status of the fetus
- Emotional trauma associated with a termination following a much desired pregnancy
- Health risks associated with possible repeated terminations
- The live birth rate for PGD may be better compared to the live birth rate for conventional IVF, particularly if only 1 embyro is replaced (SET). This is preferred and regularly reduces pregnancy with issues with multiple gestations
What are the concerns associated with the use of PGD/PGS?
Both techniques can only be used in conjunction with IVF. Despite the relatively wide acceptance of PGD/PGS in the clinical arena, it remains a technically demanding procedure. PGD involves the use of highly technical molecular biology techniques. Fortunately the error rates are likely to be less than 2%. While PGD/PGS is diagnostically reliable, we still advise all patients to undergo prenatal diagnosis (amniocentesis or CVS) to ensure that the pre-implantation diagnosis is accurate, and to test for any abnormalities not screened for during PGD.
What are the ethical issues associated with PGD/PGS?
Discarding affected embryos
PGD/PGS involves making a decision about the fate of affected embryos prior to pregnancy, at a very early stage of development. This is in contrast to prenatal diagnosis, which requires a decision to be made about terminating an existing pregnancy, at a much later stage. For many people, discarding embryos is likely to be ethically less problematic than terminating a fetus. For others, both abortion and PGD/PGS may be unacceptable.
PGD for Human Leukocyte Antigen tissue typing
Human Leukocyte Antigen (HLA) tissue typing or tissue matching is an additional step to PGD to determine if an embryo could lead to the birth of a child who is a tissue match for an ill sibling.
For some people, HLA tissue typing raises many ethical and social questions. One of the most significant issues is whether people should be able to select an embryo on the basis that the child born may be the source of life saving therapies for a sibling.
Can PGS be used to select the sex of a baby?
Yes. The use of PGS for sex selection is carried out for two major reasons. The first is to prevent transmission of sex-linked genetic conditions, when a specific test for the condition is not available. This medically-based rationale is acceptable to most. The second reason, a social one, is to provide parents with a child of the preferred sex. We allow couples to specify sex and pursue “family balancing” after they have had at least one child of the opposite sex and have fully discussed with us the pros and cons as well as the risks and benefits of such an approach.
Can PGD be used to “design” babies?
In principle, PGD/PGS can be used to select for or against any characteristic that has a genetic origin. Some contend that PGD could be used to select against obesity, or hyperactivity, or for intelligence, beauty, or athletic ability. However, the use of PGD for these purposes is not currently scientifically possible.
For some, any selection of embryos is regarded as leading to designer babies. However, PGD does not allow people to determine the precise characteristics of embryos.
Please contact us if you have any questions. We are proud of our PGD/PGS program and our IVF success rates are world class. As a patient of ORH you can feel secure that you will receive the best care possible.