What is PGD (Preimplantation Genetic Diagnosis)?

What is PGD (Preimplantation Genetic Diagnosis)?

PGD is a specialized laboratory procedure that is performed alongside In Vitro Fertilization to identify genetic disorders in embryos before implantation.

What is PGD (Preimplantation Genetic Diagnosis)?

PGD is a specialized laboratory procedure that is also known as preimplantation genetic diagnosis. The procedure is performed alongside In Vitro Fertilization (IVF) to identify genetic disorders in embryos before implantation and pregnancy.

Who are good candidates for PGD?

PGD techniques offer various benefits for individuals who are at risk of passing on inherited conditions to their children. The PGT test can be applied to you if:

  • You have a known genetic disorder in your family.
  • You have a story of multiple miscarriages where genetic issues are generally suspected.
  • You have a child who needs a stem cell donor.
  • You are preparing for IVF, and your doctor needs to screen for chromosomal abnormalities.
  • You have had an unsuccessful IVF journey where genetic factors might be a cause.

Which Conditions Can Be Diagnosed Using Preimplantation Genetic Diagnosis?

PGD can diagnose a variety of genetic conditions that should be detected in IVF embryo transfer. The test primarily focuses on autosomal dominant, autosomal recessive, and X-linked abnormalities.

Some of the conditions that can be detected with a pre-implantation genetic diagnosis are:

  • Cystic Fibrosis: A genetic disorder affecting the lungs and digestive system.
  • Sickle Cell Anemia: A blood disorder causing red blood cells to become misshapen.
  • Tay-Sachs Disease: A rare, inherited neurodegenerative disorder.
  • Duchenne Muscular Dystrophy: A genetic disorder characterized by progressive muscle degeneration.
  • Beta-Thalassemia: A blood disorder reducing the production of hemoglobin.
  • Structural Chromosomal Changes: Such as translocations, which can affect fertility and lead to miscarriages or birth defects.
  • Mitochondrial Disorders: Though less common due to the complexity of mitochondrial heteroplasmy.

Types of Preimplantation Genetic Testing

PGD may be recommended by your fertilization specialist if you have a known genetic abnormality that might pose a risk to your children. To detect these abnormalities, your doctor may apply different genetic diagnoses to PGD types. There are mainly two types of PGD that are briefly summarized below:

FISH (Fluorescent In Situ Hybridization)

This technique is used for locating specific DNA sequences on chromosomes. FISH is particularly useful for identifying structural chromosomal abnormalities and specific gene mutations. However, it has some limitations in terms of the number of chromosomes it can simultaneously analyze.

PCR (Polymerase Chain Reaction)

PCR is one of the preimplantation genetic diagnosis types used to amplify small segments of DNA or RNA. This test type makes it easier to analyze specific genetic sequences. In PGD, PCR is often used for identifying single gene disorders.

Next Generation Sequencing (NGS)

NGS allows for comprehensive genetic screening by sequencing large portions of the genome. This method is highly effective in detecting both inherited and de novo (newly arising) genetic abnormalities. NGS can provide detailed information on chromosomal abnormalities and single gene mutations.

Microarray

Microarrays are used to examine gene expressions and copy number variations. This technology can analyze thousands of genetic sequences at once which makes it highly efficient for screening a wide range of genetic abnormalities.

The Procedure of PGD

PGD procedure involves several steps that are closely integrated with in vitro fertilisation.

Ovarian Stimulation

PGD procedure starts with stimulating the ovaries. Because enlarged ovaries can produce multiple eggs.  

Egg Retrieval

The egg retrieval process involves removing the mature eggs surgically from the ovaries. The average number of eggs retrieved IVF by age can be summarized as follows:

For women under 35, between 4 and 14 eggs can be collected, while for women 38 years old, the number of eggs increases to 10 to 34.

Insemination

After the egg retrieval procedure, the eggs are fertilized by either In Vitro Fertilization or Intracytoplasmic Sperm Injection.

Fertilization Check

The day after insemination, your doctor will check if the eggs are fertilized.

Embryo Biopsy

When embryos reach the blastocyst stage, generally a 5 day blastocyst, your doctor performs a biopsy. The biopsy process involves the removal of a few cells from the outer part of the embryo.

Embryo Testing

PGD is performed to check for specific genetic condition types.

Embryo Transfer

After the PGD, embryo transfer, or blastocyst transfer, is performed if the embryos are free from genetic conditions.

Pregnancy Test

Approximately 12 days after embryo transfer, you can conduct a pregnancy test to confirm blastocyst implantation.

Would Preimplantation Genetic Diagnosis Guarantee the Birth of A Child Without My Condition?

PGD can increase the likelihood of having a child without a specific genetic condition. The accuracy of embryo testing is generally high; however, this can vary depending on the specific condition being tested for.

You should note that even if there is a low risk of misdiagnosing the condition, the chances still exist. In addition, a preimplantation genetic diagnosis cannot guarantee the overall health of your child or rule out all potential genetic issues. To conclude, after PGD IVF, you should take into consideration that the test does not offer a definite guarantee.

 

Faq

Who is eligible for a preimplantation genetic diagnosis?

PGD is recommended for you if you are at risk of passing on your genetic disorders to your children. For example, when you check your family history, you may come across genetic diseases or chromosomal abnormalities. In this case, your doctor should perform PGD to check the healthy embryos. On the other hand, if you have had multiple pregnancies that were unsuccessful, genetic factors should be evaluated as well.

What is the difference between PGD and IVF?

In Vitro Fertilization (IVF) and preimplantation genetic diagnosis are two different procedures. While IVF is a process where eggs are fertilized by sperm outside the body to create embryos for implantation, PGD is an additional procedure used to test these embryos for specific genetic disorders.

What is the biological concept of PGD?

The biological concept of preimplantation genetic diagnosis consists of analyzing the genetic heredity of embryos created through blastocyst IVF before they are implanted in the uterus. This test is done to identify genetic defects within embryos to prevent certain genetic diseases or disorders from being passed on to the child.

In PGD, a few cells are taken from the embryo and tested for specific genetic conditions or chromosomal abnormalities. The process helps in selecting genetically healthy embryos for implantation. Lastly, embryo testing thereby increases the likelihood of a healthy pregnancy and reduces the risk of genetic disorders in the offspring.

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