PGD/PGS: testing of genetic equipment of the embryos before transferring to the uterus
The biggest wish of every parent is to have a healthy baby. Thanks to determining the genetic equipment of embryos we can detect problems in time. Then we transfer into the uterus only healthy embryos that have potential of a successful pregnancy.
Genetic abnormalities are a frequent cause of early miscarriages in the first third of the pregnancy. Preimplantation diagnosis helps prevent these losses.
Parents with genetic load have PGD done
- The method is called preimplantation genetic diagnosis – PGD.
- It is suitable if one or both partners have a genetically conditioned disorder in the family.
- In the diagnostics, we focus on the chromosomes that carry information about the defect. For the transfer to the uterus we choose only those embryos that did not inherit bad genes.
Healthy partners choose PGS
- The method is called preimplantation genetic screening – PGS.
- Parents who are healthy order it preventively. Often these are cases in which previous IVF failed.
- We will test selected or all chromosomes.
What can we detect using preimplantation diagnosis?
- Down syndrome (trisomy 21)
- Edwards’ syndrome (trisomy 18)
- Patau syndrome (trisomy 13)
- Turner syndrome (monosomy X)
- Klinefelter’s syndrome (trisomy XXY)
Gene mutations causing:
- cystic fibrosis
- fragile X syndrome
- sickle cell anemia
- Alport syndrome
- mutation of tumor suppressor gene p53
- neurofibromatosis type I
Determining the sex of a child whose mother is a carrier of a disease manifested only in boys:
- hemophilia A and B
- ectodermal dysplasia
- fragile X syndrome
How does the PGD/PGS work:
- First we wait for 72 hours after fertilization for the embryo to have a greater number of cells.
- We gently separate one or more cells and analyze them.
- The analysis is carried out by various methods – FISH (fluorescence in situ hybridization) aCGH (microarray, comparative genomic hybridization), PCR (polymerase chain reaction).
- The geneticist presents the results within 48 hours.
- The embryo is not damaged by this intervention and continues in its development.
- We will recommend the best embryos for the transfer to the uterus after evaluating the results.
The analysis reveals most of the problems
Thanks to this analysis you will significantly reduce the risk of a miscarriage or giving birth to a sick child. However not even PGD / PGS are able to detect everything, and the results of the genetic tests are not 100% right. This is for several reasons.
The genetic profile of an embryo is based on the principle that all cells in the human body contain the same chromosomal equipment. However, there are diseases or conditions where the cells are so-called mosaics. This means that the defect occurs only in a few percent of cells.
In this case it matters which cell the geneticist gets under the microscope for the preimplantation diagnosis. Fortunately, such cases are not numerous and geneticists take them into account. Therefore the geneticists mention these illnesses which are only found in a few percent of the cells with a certain probability. Another disadvantage of this examination is that only certain diseases are tested.
Therefore the preimplantation diagnosis does not replace prenatal screening for congenital defects. When doing PGD we trace only a disease that is already in the family. A different one can however occur to the baby. The prenatal screening, which is carried out between the 10th and 20th week of gestation, can reveal such problems as Down syndrome and others.
Recommendation for PGD/PGS examination in these cases:
- Repeated miscarriages.
- Frequent unsuccessful IVF cycles.
- Premature childbirth or a miscarriage of a child with a chromosomal defect.
- Age risk (maternal age over 36 years).
- Defects connected with a person’s sex when unaffected individuals are purposefully chosen.
- For sperms obtained by surgical sampling (MESA / TESE).
- One of the parents is a carrier of a specific gene shift (probes for such couples are very individual).
- Some common genetically well diagnosable diseases such as cystic fibrosis, fragile X syndrome, hemophilia, thalassemia, sickle cell anemia, phenylketonuria, mutation of tumor suppressor genes.
- For couples whom only a small number of embryos managed to be fertilized.
Experience of foreign experts
Professor Alan Handyside has largely contributed to the development of the PGD method and its introduction into clinical practice in the UK in the early 90s of the 20th century. The first PGD pregnancy in Central Europe happened right in the Czech Republic in 2001.
On the 25th anniversary of the establishment of the method Professor Handyside summarized the existing results in this presentation presentation (click to read the presentation, which is in the Summary section on his LinkedIn profile). We can see there that PGD actually has a great influence on carrying a fetus to term. Less than 50% of women gave birth to a live child after undergoing IVF in 2012. However, when the doctors performed preimplantation diagnosis and chose only the most suitable embryos, the success rate rose to 65%.
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