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Apr 12

PGD / Genetics

Preimlantation Genetic Diagnosis (PGD) is a state of the art technology with potential to increase your chance of a healthy pregnancy. PGD is used to identify genetic defects in embryos created through in vitro fertilization (IVF) before transferring them into the uterus. PGD is recommended when embryos may be affected by a certain genetic condition and it is offered to fertile and infertile couples in conjunction with IVF.

PGD is a means to genetically analyze a single cell from an 8-cell embryo (biopsy) in order to determine more accurately if it is normal. Only healthy and normal embryos are transferred into the mother’s uterus for implantation, thus preventing adverse outcomes such as miscarriages, pregnancy termination (after positive prenatal diagnosis, i.e., amniocentesis or chorionic villus sampling), or birth defects (physical and/or mental).

The use of PGD it just avoids the problem of inadvertently transferring abnormal embryos back into the woman, while freezing the normal ones, because they all “appear” similar. Due to the complex and sophisticated technology and expertise involved there relatively few laboratories who offer PGS/PGD programs. Fortunately, in our center we have incorporated this state of the art technology for PGS and PGD for structural rearrangements and we offer it as an option for anyone in need.

What is PGS/PGD

pgd1The major application of PGD in the field of assisted reproduction is seen in aneuploidy screening and diagnosis of unbalanced parental inheritance of chromosome abnormalities (translocations, inversions). The most common type of PGD today involves testing of embryos for a panel of the most common chromosome abnormalities (aneuploidy screening) and selecting only normal embryos for embryo transfer. Each IVF cycle, therefore, has a better potential outcome, since embryos screened in this way have a higher rate of implantation in the uterus, lower spontaneous loss rate, and a reduced risk of trisomic offspring (i.e. Down syndrome).

Application of PGD

Many couples have benefited from the use of PGD. If you answer yes to any of the following questions, PGD may be helpful for you.

  • Are you a woman over 35?
  • Have you experienced several miscarriages?
  • Have you had a prior pregnancy with a chromosome abnormality?
  • Have you experienced several failed IVF cycles?
  • Has conceiving been difficult due to a low sperm count?
  • Do you or your partner carry a balanced structural chromosome rearrangement?
  • Do you or your partner carry an X-linked genetic disease such as hemophilia or Duchenne Muscular Dystrophy?

When and how PGS/PGD is performed?

pgd2-300x225Following fertilization, embryos grow in culture for further 3 days until they reach the 8-10 cells stage. At that time the embryo is at the cleavage stage, and one or two cells may be carefully removed for genetic analysis without causing any damage to the future development of the embryo. With the embryo held still by gentle suction using the holding pipette, an opening is made in the outer shell, called the zona pellucida, using laser. Afterwards, a micropipette aspirates carefully and very gently a single cell (blastomere). At this early stage of embryo development, all of the cells have the same potential for development, therefore, removal of one or two cells from the embryo is not detrimental and the embryo can continue its normal development following the procedure. The cell that has been removed is then fixed on a glass slide and it will be subjected to chromosomal analysis for specific chromosomes. The most common type of PGS/PGD today involves testing for a panel of the most frequent chromosome abnormalities found in miscarriages and live born babies (chromosomes 13, 16, 18, 21, 22, X and Y). Following biopsy, embryos are kept in culture until they are ready for implantation (day 5 after fertilization). Only chromosomally normal embryos will be transferred to the uterus for implantation.

pgd3-300x225PGS/PGD of chromosomes is performed with Fluorescence In Situ Hybridization (FISH) technique by which small pieces of DNA (probes), are specifically bind (hybridize) to certain regions of the chromosomes being analyzed. Each probe is labelled with a different fluorescent dye. These fluorescent probes are applied to the cell nucleus of the cells taken by biopsy and are expected to hybridize to the specific chromosomes. Using a fluorescent microscope the geneticist can visualize the fluorescent colour signals for each chromosome type present (one, two or more signals). A single fluorescent signal represents a monosomy, two signals a disomy (normal) and three signals a trisomy of the specific chromosome. In this way the diagnosis of aneuploidy of the specific chromosomes is performed.

Benefits of PGS/PGD in most infertile couples
To increase the pregnancy rate by determining more accurately which embryos to implant in the woman, which to freeze, and which to discard as non-viable.
To reduce the risk of miscarriage.
To better counsel patients who do not produce any normal embryos (who might need thereby to consider donor eggs so that they don’t waste time, emotion, and energy on multiple cycles that fail to produce a viable pregnancy).
To encourage couples who have failed to get pregnant, but whose embryos are “chromosomally normal“.
To reduce the number of embryos that has to be transferred so as to reduce the risk of triplets or quadruplets.

Indication for PGS
Advanced maternal age (over 35).
Couples with repeated miscarriages.
Couples who have experienced several IVF failure.
Couples who have had a prior pregnancy with a chromosome abnormality.
Men with infertility requiring intracytoplasmic sperm injection (ICSI).
Men with positive aneuploidy sperm screening.
Couples where at least one partner is an aneuploid mosaic.
Couples where at least on partner is a carrier of an X-linked disease.

Indications for PGD for structural chromosomal rearrangements

Couples where at least one partner is a carrier of a structural chromosomal rearrangement (translocation, inversion, deletion).

Concerns and disadvantages

Nevertheless there are some concerns or disadvantages for using PGD:

  • Fertile couples must undergo IVF to produce suitable embryos
  • Technical problems might occur during blastomere biopsy or preparation
  • Even with a successful IVF and PGD procedure, pregnancy is not guaranteed after transfer, nor is a term or near-term delivery
  • Analysis of a single cell has limitations and misdiagnosis resulting from mosaicism (when the embryo has cells with different compositions) may occur. For this reason, prenatal diagnosis should confirm the condition of the fetus
  • Not all chromosomal or genetic abnormalities can be diagnosed with PGD because only a restricted number of chromosomes can be examined at on time during the course of a single procedure
  • Currently, only a specific examination of a single biopsied cell is available. A single cell cannot be screened for multiple genetic conditions

The use of PGD just avoids the problem of inadvertently transferring abnormal embryos back into the woman, while freezing the normal ones, because they all “appear” similar. Due to the complex and sophisticated technology and expertise involved there are relatively few laboratories who offer PGS/PGD programs. Fortunately, in our center we have incorporated this state of the art technology for PGS and PGD for numerical and structural rearrangements and we offer it as an option for anyone in need.

Karyotype evaluation

pgd4-236x300Cells, in their nucleus, contain string-like structures called chromosomes where all of our genetic material (genes) resides. Genes are made up of DNA sequences. Each cell has approximately 30.000 genes. Abnormalities in gene function cause genetic diseases. This may occur by having too many or too few chromosomes (aneuploidy), when chromosome pieces are attached to the wrong chromosome (translocation), when a chromosome is missing a piece of it (deletion), when part of a chromosome is upside down (inversion) altering its natural structure, or when a gene’s DNA sequence is altered.

Chromosome abnormalities

All somatic cells contain 23 pairs of chromosomes (46 chromosomes in total) of which, chromosomes 1 to 22 are called autosomes and chromosomes X and Y are called sex chromosomes. Sperm and egg (gametes) contain 23 single chromosomes, one of each chromosome pair. During fertilization the embryo receives one set of all chromosomes from each parent resulting in a normal male 46,XY or in a normal female 46, XX. If the sperm or egg enclose a chromosome abnormality, it can be passed on to the embryo resulting in a genetic disorder.

Chromosomally abnormal embryos conceived naturally or through IVF, have a low implantation rate. Still, if they do manage to implant, the pregnancy often results in miscarriage or the birth of a baby with chromosome disorder. Over half of all first trimester pregnancy losses are due to chromosomal abnormalities.

When & why?

Reproductive failure refers to both the inability to conceive (infertility) as well as the inability to carry a pregnancy successfully to term (spontaneous abortion, recurrent abortion). Embryos that do not carry a full chromosomal component are likely to be lost soon after implantation or they do not implant at all. Karyotyping (test of the chromosome number and structure) of the parents is now routinely used for the management of recurrent abortions. Infertility is another form of reproductive failure, and genetic screening plays an increasingly important role in its evaluation. It is well known that the incidence of chromosomal abnormalities is significantly elevated in couples with fertility problems.

In our center we perform cytogenetic investigation in couples with:

  • Recurrent miscarriages
  • Unsuccessful IVF cycles
  • Unexplained infertility
  • Male infertility

Where does cytogenetic analysis help?

  • In the establishment of a diagnosis
  • In the establishment of the exact genetic aberration
  • In the establishment of the pattern of inheritance of the specific genetic aberration

Treatment can then be tailored to fit each patient’s medical background and the type of chromosomal changes he/she may possibly carry. Treatment may include pre-implantation genetic diagnosis (PGD), for those selected cases where PGD could identify the healthy embryos improving the final outcome, additional IVF attempts, or oocyte/sperm donation whenever indicated.

Our Prices

In Vitro Fertilisation (IVF) Cycle with own gametes from 1300€

Gametes Donation from 2600€

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