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Preimplantation Genetic Testing (PGT)
Preimplantation genetic testing refers to the genetic testing of embryos prior to when they are placed in the uterus. PGT commonly done is preimplantation gentetic testing for aneuploidy which had been formerly known as PGS preimplantation genetic screening. Aneuploidy refers to abnormalities in the full complement of chromosomes in each cell, i.e. 46XY or 46XX. Understandably one can have additional or missing chromosomes so as not to have 23 intact pairs. This is the most common cause of failed implantation or miscarriages. PGT-M is less commonly done but is vital to eliminate inherited diseases from a family tree. Preimplantation screening metabolic (formerly known as PGD preimplantation genetic diagnosis) is done to determine whether cerain genetic diseases such as in-born errors of metabolism or single gene disorders are present. For a partial list please see below. PGT-A/PGT-M (formerly known as PGS or PGD respectively) involve the same technique for the removal of a cell from an embryo that was created using In vitro fertilization (IVF).Both these tests can be performed on the same biopsy sample using state-of-art nucleotide sequencing platforms managed with artificial intelligence (Gindoff P, Alouf C, Gindoff I. Fertil Steril 112: 647, 2019) essentially revolutionizing the field of IVF. Lastly PGT-SR preimplantation genetic testing can be performed for structural rearrangeaments of chromosomes, a much less common cause of pregnancy failure. These are commonly referred to as reciprocal translocations and inversions which can be present in the parents and passed to the child. Now that we are up to date on the nomenclature we can explore some more details.
PGT-M
PGT-M, is a diagnostic procedure in which embryos are tested for genetic abnormalities. Screening for a genetic illness can be done by performing PGT-M for a single gene mutation. In this situation, the embryos are screened not for a chromosomal problem, but for a single gene abnormality associated with a single disease. Thousands of gene loci have been identified. Certain illnesses are carried as traits by parents. When both traits are passed on to a child, she or he can be affected. Yet, for many such illnesses, carrier status can be diagnosed prior to conception. Both family history and ethnic background help to determine which testing may be appropriate for you. PGD screenings for single gene defects have been carried out for scores of genetic illnesses, including: cystic fibrosis, Huntington’s chorea, Marfan syndrome, Tay-Sachs and Sickle Cell Anemia.
PGT-A: Preimplantation Genetic Testing for an Aneuploidy
PGT-A, Preimplantation Genetic Testing for an Aneuploidy (formerly known as PGS) is when embryos are tested for chromosomal abnormalities. Chromosomes are sub-cellular structures that house one’s genes. All of the information that is needed to lead to an individual’s development is contained on these chromosomes and each one of us has 23 pairs of them. During human reproduction, it is not unusual to produce embryos that have too few or too many chromosomes, this is known as “aneuploidy”. PGT-A is used to screen for commonly encountered embryonic chromosomal disorders. Infertile couples may benefit from this test if the female partner is older, if they have had several failed IVF cycles, or if they suffer from repetitive older miscarriages. For example, Down’s Syndrome is such a disorder where there is an extra chromosome #21, making the cell have three of chromosome #21 instead of just a pair.
How to Determine if You Need PREIMPLANATION GENETIC Testing?
The physicians of Chelsea Fertility NYC have long-term experience as they are some of the first in the field to utilize this technology and are published in this area as well. At Chelsea Fertility NYC, we perform PGS (PGT-A, PGT-M, PGT-SR) as indicated:
- (A) PGT-M: Patients with in-born errors of metabolism (i.e. Tay-Sachs, Gaucher’s)
- (B) PGT-M: Patients that carry genetic markers for known diseases (i.e. cystic fibrosis, hemophilia, sickle cell anemia, muscular dystrophy, etc.)
- (C) PGT-A: Patients with unexplained miscarriages (over 70% of repetitive miscarriages are due to aneuploidy)
- (D) PGT-A: Embryo screening to de-select aneuploidy electively and optimize implantation attempts and efficiency
- (E) PGT-A: Gender identification in normally screened embryos
- (F) PGT-A: Improve implantation when egg quality or sperm quality is compromised from advancing age or environmental toxicity exposure
- (G) PGT-A: Improve implantation in PCOS patients undergoing elective frozen embryo transfer
- (H) PGT-SR: Reserved for known translocations or inversions in parents that cause miscarriages that need to be de-selected to allow implantation
The PGS
The embryo is developed for five days in the lab after egg harvesting and fertilization. The outer area of cells, known as the trophoblast ((placental cells) is biopsied. A few cells are removed from over one hundred at this location. The embryo is not harmed or compromised, but occasionally its growth may be arrested. For (PGT-MD) genetic diseases,- the cells are analyzed for markers of these diseases. The embryos are frozen while awaiting results, which can take a few days. Once the normal embryos that do not carry the genetic disease are identified, the embryos can be subsequently warmed or thawed and transferred back without any decrease in success from being frozen due to advanced freezing technology known as vitrification. For (PGT-A) aneuploidy screening , the cells are analyzed within days with results of all 23 chromosomes including sex chromosomes. This assessment of the integrity of the chromosome composition of the embryo allows for a more correct decision as to what embryo to transfer. The embryo is also best frozen and transferred during a subsequent cycle. *Please note that if needed, both PGT-M and PGT-A can be done on the same biopsy.
Talk to Your Fertility Specialist about PGT-M/PGT-A/PGT-SR
The fertility specialists at Chelsea Fertility NYC have extensive clinical experience with Preimplantation Genetic Testing options, including PGT-M and PGT-A and PGT-SR. The initial step involves in-depth testing and analysis to determine the indication for these options and to review alternatives. We invite you to contact Chelsea Fertility NYC to request an initial genetic testing consultation. The lab and medical staff at Chelesea Fertility NYC also has recognized publications in peer review journals in the field and serve as on editorial boards in leading journals in the field of IVF, pharmacogenomics, artificial intelligence in IVF, and PGS.
Frequently Asked Questions about PGD/PGT-A:
Can PGD/PGT-A help improve IVF success rates?
This is a controversial issue as patient selection (age, indication) does determine its efficacy. PGT-A or PGD can cause a transient stunting to the growth of the embryo and may decrease the overall pregnancy rate in young patients (less than 35 years of age) who would otherwise not need this procedure. For this reason, PGD/PGT-A screening(s) are not routinely done unless there is a history of repetitive pregnancy loss (miscarriages) in the younger patients or a medical indication for PGD. For all patients with RPL, regardless of age, this can increase the chances of a live birth.
PGD is done for genetic disease removal from the embryo so the resultant child will not be afflicted, and therefore is indicated when the goal is to do so. Older patients with increased risk of aneuploidy may benefit from PGT-A as well. Your physicians at Chelsea Fertility NYC are experienced with this and fully understand the complexities and value of PGD/PGT-A. We will make sure you are informed completely to allow you to make the best decision in your management.
How much is PGD/PGT-A? Can the cost be covered by insurance?
This is a variable among providers, but Chelsea Fertility NYC center does offer competitive packages to consider should your insurance not cover this service.
Are there any risks involved with PGD/PGT-A?
To date, there are no known risks associated with the procedure that would add to the risks associated with infertility or IVF in general.
Do PGD/PGT-A replace prenatal testing?
We would still advise amniocentesis or chorionic villus sampling as indicated for the pregnancy.
Can PGD/PGT-A be used for gender selection?
Yes, PGT-A is used for screening out genetic abnormalities, such as chromosomal abnormalities and documenting the gender and normalcy of the sex chromosomes.
What is the difference between PGS and PGT-A?
There is no procedural difference between PGS and PGT-A. PGT-A reflects the nomenclature transition within the fertility community. We invite patients to learn more about PGT-A in our blog.
PGD: Suggested Genetic Screening
By Ethnicity:
- Northern European
- CF- molecular testing for common mutations -specify ethnicity
- African:
- Sickle cell Anemia-hemoglobin electrophoreisis
- Alpha-thalassemia-Complete blood count for MCV
- Beta-thalassemia-Complete blood count for MCV
- Caribbean or Latin American:
- Sickle Cell Anemia-hemoglobin electrophoreisis
- Southeast Asian
- Alpha- thalassemia-Complete blood count for MCV
- Beta-thalassemia-Complete blood count for MCV
- Indian or Pakistani:
- Beta-thalassemia-Complete blood count for MCV
- Sickle cell Anemia-hemoglobin electrophoreisis (Indian)
- Middle Eastern
- Sickle cell Anemia-hemoglobin electrophoreisis
- Mediteranian (Sardinia and Cyprus)
- Beta-thalassemia-Complete blood count for MCV
- Sickle cell Anemia-hemoglobin electrophoreisis
- French Canadian/Acadian:
- CF-molecular testing for common mutations (specify ethnicity)
- Tay Sachs Disease-serum hexaminodase level
- Ashkenazi Jewish-consider genetics counselling:
- CF-molecular testing for common mutations (specify ethnicity)
- Tay Sachs Disease-serum hexaminodase level
- Canavan Disease-molecular testing for common mutations (specify ethnicity)
- Gaucher Disease- molecular testing for common mutations (specify ethnicity)
- Niemann-Pick
By Condition:
- Cystic Fibrosis
- Ashkenazi Jewish
- French Canadian
- Northern European Caucasion
- Alpha-Thalassemia
- Southeast Asian
- African
- Beta-Thalassemia
- Mediteranian (Sardinia and Cyprus)
- Southeast Asian
- Indian (East)
- Pakistani
- African
- Sickle Cell Anemia
- African
- Mediteranian (Sardinia and Cyprus)
- Middle Eastern
- Caribbean
- Latin American
- Indian
- Tay-Sachs
- Ashkenazi Jewish
- French Canadian/Acadian
- Canavan Disease
- Ashkenazi Jewish
- Gaucher Disease
- Ashkenazi Jewish
- Niemann-Pick