Preimplantation genetic diagnosis screening (PGD) helps to identify genetic defects within an embryo before implantation. This method serves as a layer of defense against specific disorders or diseases which could affect the child later on in life. Most embryos which go through PGD come from the in-vitro fertilization (IVF) process.
The PGD procedure is straightforward by design. The genetic diagnosis starts with the IVF procedures, including fertilization and egg retrieval within a laboratory environment. Then the embryo begins to divide into multiple cells over the next 3-5 days. That is when the screening process occurs.
There are 4 steps followed when implementing the preimplantation genetic screening process.
- Cells are surgically removed from the embryos for analysis. After collection, each embryo is then frozen safely in storage.
- The DNA of the extracted cells undergo an evaluation to determine if they inherited a problematic gene from one of both biological parents. This step requires about one week to complete.
- When PGD screening identifies no genetic concerns, the embryo will then be placed in the uterus, waiting for implantation and a positive pregnancy result.
- Additional embryos which screen out as clear of genetic concerns remain frozen in safe stasis for later use. Any with problematic genes going through a formalized destruction process.
Here are the preimplantation genetic screening pros and cons to evaluate if you’re pursuing IVF or have concerns about passing problematic genes along to future offspring.
List of the Pros of Preimplantation Genetic Screening
1. The PGD screening process benefits many couples.
You can identify embryos at risk of developing genetic diseases or conditions with the preimplantation genetic screening process. Couples who have sex-linked genetic disorders, are carriers of single-gene disorders, or have chromosomal disorders all receive information through this testing to ensure their offspring are healthy. Women over the age of 35, those who experience recurrent pregnancy loss, and women with failed fertility treatments in the past benefit from PGD screening too.
2. It tests for more than 400 different genetic conditions.
The preimplantation genetic screening process detects genetic conditions based on the profiles of the donating biological couple. A complete list of the PGD testable diseases is available through The Fertility Institutes if you have health concerns in this area. Your doctor may recommend specific tests from your medical file. You may also have the opportunity to request your own tests if there are particular concerns about your family history.
3. The screening process occurs before implantation.
The embryos are not harmed by the preimplantation genetic screening process. Their cells are surgically removed during the initial division process, allowing more to be created as the embryo begins to grow. That means the PGD screening occurs before implantation. The information provided by the testing results enable a couple to determine if they wish to continue with their attempts at a pregnancy before causing one in the first place. That limits the issues of treating dangerous, even life-threatening, genetic disorders or diseases for some couples.
4. The PGD screening process allows more couples to have biological children.
Without preimplantation genetic screening, the risk factors for having future offspring with a health issue are quite high. If a biological parent has an autosomal dominant disorder, then there is a 50% risk of inheriting the gene. With autosomal recessive disorders, the risk is 25% for each pregnancy for a health issue, and a 50% risk that the child will become a carrier.
X-linked dominant conditions have a 50% chance of being passed along, as do X-linked recessive disorders. Boys have a chance of receiving a Y-linked inheritance disorder. Each pregnancy assumes these risks. Thanks to PGD screening, the issues are detected before the embryo fully develops, allowing parents to avoid these health concerns in their children.
5. PGD screening reduces the risk of a multiples pregnancy.
The preimplantation genetic screening process identifies healthy embryos for implantation. Instead of implanting several at once in the hopes that one will attach to create a positive pregnancy, PGD encourages singular implantation efforts for viable embryos instead. That may reduce the chances of becoming pregnant for some couples. It may also reduce the risk of having twins, triplets, or more when undergoing IVF procedures.
The overall rate for having twins without IVF is 3.35%. With gonadotropins therapy, the rate increases up to 30%. Using Clomid and Femara raises the risk of having twins to 12%. IVF under the age of 35 creates an overall risk of 12.1%.
6. The screening process increases the chances of a successful transfer.
Healthy embryos transfer better to become a successful pregnancy compared to unhealthy embryos. When cell development is abnormal, the human body often rejects the attempt to attach or implant to create a successful pregnancy. That is why some women have multiple embryos implanted without results, while other women have multiple gestations. Since pregnancies involving multiples creates risks for the mother and the growing embryos, as does the development of a non-viable embryo, preimplantation genetic screening increases the potential of a successful singular transfer.
7. Detection of genetic abnormalities occurs earlier than in other treatment options.
The preimplantation genetic screening process allows doctors to pinpoint genetic problems occurring with an embryo before it is transferred to the uterus. You’ll now after six days of development in most situations whether or not you have any potential embryos for transplantation. Although destruction is the usual procedure for embryos which have abnormal chromosomal profiles, couples are given the option to freeze them instead in the hopes that a cure in the future for the genetic disorder or disease detected allows for viable human life potential.
8. It can reduce the financial burdens of the couple trying to have children.
The costs of preimplantation genetic screening are admittedly high. When compared to the cost of treating a child born with a genetic disorder or disease, however, PGD helps families to save money. Some may experience high levels of affected embryos when tested, which stops them from having additional costly IVF cycles. The discovery of multiple affected embryos when there are extensive genetic concerns with one or both parents allows for healthy unaffected donor eggs and sperm to be used too.
9. The final decision to proceed is still yours.
The preimplantation genetic screening process allows doctors to provide you with more information about the potential viability of your embryos. They will recommend that you not proceed with any transplantation procedures involving an abnormal result. You still have the final say, however, as to what you want to have happen. That means some couples can plan for the gender of their child, especially older parents who may want to have a boy and a girl. It also means you can address the needs of any abnormal embryos in a way that works for your feelings, spirituality, and core beliefs.
10. There are lower risks of a miscarriage with PGD.
Because healthy embryos are transferred as part of the IVF process (or other forms of reproductive treatment), women have a lower overall risk of experiencing a spontaneous abortion with preimplantation genetic screening. According to IVF1, about 8% of the couples who choose PGD as part of their treatment experience a miscarriage after the transplantation procedure is successful. The risks of this issue occurring for a couple drops by 50% in total.
Studies that use a 5-chromosome panel for PGD detect about 30% of the abnormal embryos which would cause a miscarriage. When using nine chromosomes for the panel, detection rates climb to as high as 75%.
11. PGD screen can identify health issues in the parents.
Couples who struggle to conceive may have genetic health concerns without realizing what is going on. Some issues cause adult-onset symptoms, such as familial adenomatous polyposis, which may not be discovered until the middle age years because of polyp growth. Going through preimplantation genetic screening with a full screen profile, though costly, can identify genetic issues that involve one or both parents. That information then makes it possible for a couple to seek out their own healthcare options while pursuing reproductive treatments at the same time.
12. It offers hope after multiple failed attempts.
Patients who struggle to become pregnant find hope with PGD screening because it offers information as to why there is an issue becoming pregnant. Women who are 38+ in age and having IVF find that the data allows them to make better future health decisions. As women age, the likelihood of a chromosomal abnormality increases, reaching almost 90% by the age of 44. By testing the chromosomes before a transfer,
List of the Cons of Preimplantation Genetic Screening
1. PGD screening takes time to produce results.
If you’re going through the preimplantation genetic screening process, then you must have patience with it. From start to finish, it could be 4 weeks or more before you have the answers you want. You must go through the egg retrieval process, collect sperm, and then have a successful fertilization. Each embryo requires five days of development in most situations, though some cells can be surgically removed after 72 hours. Then there are up to 14 days of testing, then an appointment to discuss the results with your doctor.
2. It can be used to select the gender of the child.
The preimplantation genetic screening process has been used in the past for the purpose of selecting the gender of the future offspring. Discarding embryos because they don’t meet the expectations of the couple involved creates an ethical question for the medical community. Although gender selection is legal in the United States, it is illegal in other nations. 43 countries currently outlaw the practice.
3. Unviable embryos are always destroyed by the PGD screening process.
This disadvantage of preimplantation genetic screening involves when individuals believe that life begins. A full list of definitions published by Princeton regarding life beginning at conception is available for review, as is a full commentary about why the definition of life published by the Times Union regarding why it may not start at conception. If you agree more with the former than the latter, then the idea of embryo destruction, even if classified as non-viable, creates an ethical issue for those involved.
At the very least, the PGD screening process does stop the potential for human life. Some would argue that the quality of life for non-viable embryos developing to birth is questionable at best. Others would say that termination before determination prevents knowing any outcome and is wrong.
4. PGD screening does not eliminate the risk of conceiving a child with a genetic disorder.
Even with 400+ genetic tests possible through preimplantation genetic screening, there is still a risk that false results or unknown conditions make it through this layer of defense. The risks of doing so are greatly diminished, however, which is why couples identified as carriers often go through this process. Gender testing isn’t even perfect with PGD screening, though some estimates place the accuracy of that process at 99.8%.
If you approach preimplantation genetic screening thinking that perfection will happen, then it is best to check your expectations at the door. PGD screening is a tool which offers information with a high degree of accuracy, but it is not currently 100% accurate.
5. The costs of preimplantation genetic screening are quite high.
The cost of preimplantation genetic screening is high because the procedure is complex. Plenty of laboratory work is necessary to complete the process. Testing for the first four embryos can be about $2,500, with some providers charging more than $5,000. Additional embryos are then tested at a discounted rate. Some IVF providers include the cost of PGD screening with their full-cycle services.
If there is a specific genetic abnormality to detect within the embryo’s cells, then a probe may need to be developed to generate that information. The cost of this service may be $5,000 or more, depending on the genetic mutation, disease, or disorder tested for at the time.
6. There may not be any successful embryos to transfer.
The preimplantation genetic screening does not offer any guarantees. Couples who have genetic carrier issues may discover after the costs of testing that no “normal” embryos were created through the process. That doesn’t mean more attempts are impossible, but it does mean that the costs for collection and testing yielded no results. Since IVF is not always covered by health insurance, spending upwards of $20,000 to get nothing back in return can have devastating consequences for the finances of some couples.
7. Some embryos never become viable for cell extraction.
The preimplantation genetic screening works only when an embryo goes on to become a blastocyst. Even healthy embryos don’t always reach this stage. Older patients often struggle with this step of the process because they have fewer eggs, which means there are fewer opportunities to reach a result.
8. The PGD screening process may damage the embryo.
Although the process of cell extraction for preimplantation genetic screening is considered safe and effective, about 1 in 5 embryos are damaged by the biopsy. When this happens, the embryo usually stops growing, refusing to proceed to its next growth phase. Should this occur, then the embryo will not create a viable pregnancy. Couples should speak with their treatment provider before PGD screening to understand this risk, and to know when they should move forward or not.
For most couples, the benefits of preimplantation genetic screening outweigh the risks involved with this potential disadvantage.
9. There is a higher risk of mitotic errors forming.
According to Dr. Richard Paulson, the preimplantation human embryo “represents an unusual life form whose biology is still not quite understood.” When the embryo reaches the blastocyst stage, the division rates become very high compared to natural development. That speed increases the risk of mitotic errors forming, along with mosaic aneuploidy, even when the inner cell mass has the exact multiple of the haploid number of chromosomes it should. Every step in the preimplantation genetic screening can be completed correctly, and these errors would still exist.
10. No significant studies about false testing results are available.
There is always the possibility that a false positive or false negative test could occur when using PGD screening. These results increase the risk that a viable embryo would be inadvertently discarded. At this time, only one clinical trial has sought to address the issues of false positives found during the preimplantation genetic screening process. Although there is a lot of information available regarding the potential value of this procedure, the disadvantages tend to receive much less attention.
The pros and cons of preimplantation genetic screening are vital points that each couple must work through with their doctor. It may provide solutions for some couples when none existed before. There are also ethical concerns which must be weighed, along with the overall cost of the process. If you are concerned about passing along a genetic disorder or disease to your future children, talking with your treatment provider about PGD is likely a good idea.