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When couples and women turn to in vitro fertilization (IVF) to treat infertility, they do so with the hope of conceiving a healthy, happy baby. After going through all of the treatment and expense of IVF, many couples want to minimize the risk of miscarriages, and passing genetic disorders to their babies. Through IVF, fertility doctors and embryologists can test embryos for disorders before transferring them. These methods are called Preimplantation Genetic Diagnosis (PGD) testing and Preimplantation Genetic Screening (PGS) testing. With these methods, fertility clinics can provide some reassurance that transferred embryos are not at risk for genetic diseases.
- PGD vs PGS Testing
- Who can benefit from PGD?
- Who can benefit from PGS?
- PGD and PGS Benefits
- Side Effects and Risks
- How is PGD/PGS performed? What is the process?
- How much does PGD/PGS cost?
PGD vs PGS Testing
PGD and PGS describe different processes, though both are related to testing for genetic abnormalities. With PGD, doctors use testing methods to try and detect genetic abnormalities in embryos because one or both parents have a genetic abnormality themselves. Hence the label, diagnosis. PGD testing looks for specific diseases, or conditions.
For example, PGD can screen for cystic fibrosis, Tay Sachs, and muscular dystrophy. The number of diseases that can be screened is wide and covers over fifty disorders.
On the other hand, fertility doctors use PGS to screen for abnormalities when neither parent has a genetic abnormality. Unlike PGD, doctors can use PGS as a broader screening. When fertility doctors use PGS testing, they look for the number of chromosomes. PGS can detect Down Syndrome.
Doctors in the UK began using PGD and PGS in the 1980s, and since then, have completed thousands of IVF cycles.
Who can benefit from PGD?
PGD and PGS make sense for women and couples who have genetic diseases, or for whose future children are at risk of inheriting one. Specially, parents who do not want to risk passing on a genetic disorder benefit.
For some women and couples, even if they do not have genetic abnormalities, PGD and PGS testing may provide benefit. Age, specific fertility issues, family history, and current health conditions may all be considered risk factors.
A 2015 article by Dr. Molina B. Dayal listed a number of risk factors that make women and couples candidates for PGD. They are:
- History of x-linked disorders. Dayal points out that x-linked diseases affect as much as 25% of couples with history of it.
- Chromosome translocations. This abnormality could result in a miscarriage as well as a number of other serious issues with the pregnancy.
- Autosomal recessive diseases(the risk of embryos with this disorder is as high as 25%)
- Autosomal dominant diseases(risk of embryos with this disorder is as high as 50%)
If couples with these genetic conditions know that they have them, fertility doctors can use PGD testing to screen for specific conditions, such as cystic fibrosis. Then, embryos that are healthy and free of the abnormalities can be frozen and/or transferred.
Who can benefit from PGS?
PGS checks for an abnormal number of chromosomes, which can result in Down Syndrome if the baby is carried to term. Most of the time, however, it leads to miscarriage or other significant pregnancy issues.
- Most couples and women benefit from PGS screening, but especially older women. Women aged 40 or over carry the highest risk of abnormal number of chromosomes in embryos, but risk is also high for women aged
- Couples and women who have tried multiple rounds of IVF unsuccessfully can benefit, too. PGS can identify abnormalities that often cause failed implantation or miscarriage
- Women who have had multiple miscarriages without explanation may also benefit from PGS.
PGD and PGS Benefits
PGD and PGS offers several benefits to those who choose to include it in their IVF cycle. First and foremost, both can reduce the risk of passing on genetic abnormalities to babies conceived with IVF. Couples going through IVF often have to go to great lengths just to become pregnant. Losing a pregnancy due to an inherited abnormality could be devastating. While PGD and PGS testing are not 100% guaranteed, they do reduce the risk.
Side Effects and Risks
Screening embryos for abnormalities comes with some risk, which is essentially the potential for embryos to be damaged in the process. When a portion of the embryo is removed for testing (a blastomere) the rest of the embryo has to stay intact. Otherwise, implantation could fail or the embryo might not survive.
Specialists, called embryologists, carefully perform the diagnostic genetic testings so that risks to the embryo are minimal. Still, ask your clinic for exact, step by step procedures and for information on how they mitigate risk.
How is PGD/PGS performed? What is the process?
PGD starts with carrier screening. Carrier screening determines whether or not one or both people carry a genetic disease. What couples and women may not realize is that neither has to have the disease in order to carry it. It is possible to be a carrier for a disease and pass it on to children, without having the disease. Carrier screening involves sending a blood sample to a lab for testing.
All screening begins with a biopsy from the embryo. Specialists perform biopsy in one of three ways.
|Polar body biopsy||The first way is called polar body biopsy. In a nutshell, this technique only works for screening female abnormalities. For this reason, specialists can biopsy the egg before it is fertilized. However, because of the limitations, specialists do not use this method often.|
|Cleavage-stage embryo biopsy||Cleavage-stage embryo biopsy is the most common procedure. This biopsy requires very careful handling to minimize risk to the embryo. During cleavage-stage embryo biopsy, specialists use microscopic instruments to extra a cell called a blastomere.|
|Blastocyst biopsy||Specialists use this procedure less often than cleavage-stage embryo biopsy, mostly because embryos cannot live very long in a lab environment for testing. The procedure is very much like the previous cleavage-stage biopsy, except that a number of cells are removed and not just one.|
Two Types of PGD/PGS Procedures
After specialists perform biopsies on the embryos or blastocysts, they screen the embryos using one of two tests: PCR and FISH.
PCR: PCR stands for Polymerase chain reaction. Simply put, PCR tests DNA for genetic disorders. PCR has limitations, especially when used with single cells like blastomeres that were extracted with a cleavage-stage embryo biopsy.
FISH: FISH stands for fluorescence in situ hybridization. The test covers a wide variety of issues, including sex-linked disorders, abnormalities, and the number of chromosomes. During the test, chromosomes are lit by fluorescent lighting, analyzed, and counted.
Post-PGD Embryo Transfer
Doctors will discuss the results of PGD or PGS, and along with the patient, determine next steps. In most cases, doctors will transfer embryos that have been cleared of abnormalities. The fertility clinic must closely monitor the timing, because they must transfer embryos while they are still viable. In some cases, none of the embryos will be cleared and because of that, the PGD will result in no embryos being transferred.
Freezing Embryos after PGD/PGS
Couples and women often ask if embryos can be frozen after PGD. The answer will vary by clinic but it is generally, yes. Embryos and blastocysts that have been screened or tested can be frozen for transfer later.
Freezing embryos after PGD provides certain benefits. First, doing so reduces the cost of subsequent rounds of IVF. Secondly, some fertility clinics suggest that implantation may be more successful with frozen embryo transfer, because the best embryos can be selected for freezing, thawing, and transfer.
Lastly, couples and women who have already frozen embryos can have those embryos thawed, tested with PGD or screened with PGS, and then frozen again.
How much does PGD/PGS cost?
PGD and PGS testing are optional, additional parts of the IVF cycle, and they add significantly to the overall cost of IVF treatment. In fact, it can cost anywhere from $4,000 to $9,000. Added to the average cost of IVF at $12,000, PGD could bring to the cost of a single round of IVF to $21,000.
The cost of PGD varies by a few things: the cost of the screening, the chosen method for biopsy, and the costs associated with testing for specific abnormalities.
Couples and women considering PGD should understand the cost and the implications, as well. For example, according the University of Rochester Medical Center, PGD doesn’t increase pregnancy rates; it reduces miscarriage rates. In other words, it does not guarantee a pregnancy or even increase the likelihood of a pregnancy. Because not all rounds of IVF result in pregnancy, couples and women should be careful to take this into consideration. Additional rounds of IVF may be needed in order to become pregnant.
Additionally, PGD may not be covered by insurance plans. However, it may be included in an installment plan by the fertility clinic. Couples and women should ask the clinic about payment options for the diagnostic or screening costs.
- PGD Facts Sheet (https://www.urmc.rochester.edu/medialibraries/urmcmedia/fertility-center/documents/pgdfactssheet.pdf)
- Preimplantation Genetic Diagnosis: Overview, Indications and Conditions, Process (http://emedicine.medscape.com/article/273415-overview)
- Down Syndrome Facts (http://www.ndss.org/Down-Syndrome/Down-Syndrome-Facts/)