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Preimplantation genetic diagnosis

Within the In Vitro Fertilization (IVF) technique there is a very important step to prevent the fetus from suffering from genetic diseases that can be avoided, this is the preimplantation genetic diagnosis: a genetic study that is carried out on the embryos before being transferred to the patient’s uterus. It has allowed healthy children to be born from this Assisted Reproduction technique.

 

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What is preimplantation genetic diagnosis (PGD)?

Preimplantation Genetic Diagnosis (PGD) consists of a genetic analysis of embryos in the early stages of their development in vitro. This technique was developed to ensure the transfer of previously diagnosed embryos as healthy and allows to obtain reports on the state of each embryo and identify possible genetic diseases that may affect the fetus once implantation has occurred.

Thanks to PGD, future diseases of which the parents are carriers can be avoided, as well as some types of cancer, so that they can ensure that the baby will be born healthy. However, it is important to differentiate between preimplantation genetic diagnosis and preimplantation genetic screening or PGS:

 

Preimplantation genetic diagnosis or PGD

Depending on the type of PGD, there are two possibilities: either the third day of embryonic development can be performed through a blastomere biopsy, an embryo cell that allows to know the embryo chromosomal endowment; or, on the fifth day after fertilization by taking cells from the trophoblast which is a layer of cells that will be part of the placenta.

This analysis allows to evaluate the embryos genetic marker for a specific hereditary disorder in order to select only the healthy embryos to be transferred to the patient’s uterus to try to achieve pregnancy.

Once the embryo cells have been extracted, the genetic analysis is carried out with a high-powered microscope to determine the trait of interest and separate the affected embryos by some chromosomal condition from those that will be transferred to the uterus through IVF.

 

Preimplantation genetic screening or PGS

Preimplantation genetic screening, PGS, is a chromosome test in which aneuploidy is detected, which consists of an abnormal number of chromosomes and is common in elderly women (40 years and older) or who have had failed IVF cycles, recurrent miscarriages, or genetically abnormal pregnancies.

PGS involves the detection of chromosomally abnormal embryos, which cause IVF failures, miscarriages or babies born with Down Syndrome (Trisomy 21) or Edward Syndrome (Trisomy 18).

 

Benefits

Before PGD, the only way to diagnose the embryos health was by amniocentesis, which left couples in the dilemma of ending the pregnancy or carrying it to term knowing that their child will suffer from some chromosomal origin condition. These reproduction techniques offer an alternative prior to pregnancy, without causing pain or discomfort to the patient.

The PGD test has been performed for more than 20 years and allows high success rates of genetic alterations detection in couples embryos who, in advance, know that they are at risk of transmitting diseases to their children. In addition, IVF success rates are higher by identifying chromosomally normal embryos for transfer.

The PGD also allows to know the sex of each embryo, which prevents the transmission of congenital diseases related to this characteristic, such as cystic fibrosis, muscular dystrophy, hemophilia or Huntington’s disease.

In summary, the benefits of this genetic analysis are: more likely to succeed with IVF, healthy children, and less likelihood of diseases related to the baby’s sex.

 

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For whom is preimplantation genetic diagnosis indicated?

In general, the PGD test is recommended to:

  • Women with a history of failed IVF cycles and maternal age over 40 years.
  • Couples in which the male has alterations in the spermatozoa meiosis.
  • Couples in which a member is a carrier of chromosomal or genetic diseases, or who is at risk of transmitting diseases to their descendants.
  • Or, with monogenic diseases, that is, in which only one gene suffers the alteration, among which are hemophilia and Duchenne disease, among many others.
  • Women with a history of miscarriage in whom chromosomal abnormalities have been detected in the embryos.

 

PGD Types

 

FISH (Fluorescent In Situ Hybridation)

Fluorescent In Situ Hybridization (FISH) is a technique in which cells or tissues DNA sequences are detected by a probe labeled with a fluorochrome, a substance that fluoresces to observe cells with an epifluorescence microscope. Although it is the most specific and sensitive technique, it should be directed towards the genomic regions that are of greatest interest, being applied mainly to the detection of deletions and duplications not visible by usual microscopic analysis.

FISH allows to detect syndromes such as Prader-Willi / Angelman, Williams, Smith-Magenis and Velocardiofacial / DiGeorge that are difficult to visualize, as well as numerical chromosomal abnormalities, rearrangements, among other abnormalities.

 

PCR (Polymerase Chain Reaction)

The PCR test or polymerase chain reaction is a chemical reaction that is used to amplify or create DNA fragments, so that they are replicated in millions of copies to study the molecules in detail in the laboratory.

 

CGH Arrays (aCGH)

Comparative genomic matrix hybridization (aCGH) is the best-known technique of PGS, which consists of a cell developing embryo analysis in order to obtain the exact number of chromosomes, so it allows to detect chromosomal syndromes and other structural changes in chromosomes.

 

What is the process like?

If the test is performed using FISH, the embryo biopsy is performed on the third day after fertilization; the process consists of extracting a cell from the embryo for a genetic study and, once the viable and disease-free embryos have been selected, the transfer can be carried out on the fifth day.

If the diagnosis will be made by aCGH, it is done on the fifth day after fertilization. Cells are extracted from the outer layer of the embryo, or trophoblast, for analysis and, once the viable embryos are selected, the embryo transfer is performed on the sixth day, or the embryos are vitrified in the blastocyst stage so that they are ready for a future IVF cycle.

Once the embryos have been analyzed, a detailed report is transmitted to the medical team in charge of IVF. They will decide the embryos that will be transferred based on their morphological characteristics and chromosomal endowment.

 

Why The Fertility Center is your best choice?

The Fertility Center is an Assisted Reproduction clinic, where in addition to having great specialists and a high human quality service, we have the most updated equipment laboratory, where procedures are carried out without having to transport embryos, eggs or sperm samples in order to maintain their maximum integrity.
With us you will have a specialists team working on the success of your case, to bring home a healthy and beautiful baby and make your dreams come true. So do not hesitate, contact us at 64 231 1020 and 858 867 4090, send us an email to hello@thefertilitycentermexico.com or contact us through our online form. We will gladly assist you!

 

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Dr. Jesús Alberto Félix Atondo

Gynecology, Obstetrics and Biology of Human Reproduction Surgeon at the Autonomous University of Guadalajara, specialist Biologist of Human Reproduction by the Mexican Institute of Infertility.

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