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Preimplantation Genetic diagnosis

Published on Aug 18, 2016 and last reviewed on Aug 26, 2022   -  3 min read

Abstract

Preimplantation genetic diagnosis helps couples have their embryos tested for any genetic abnormality before implantation. It is one of the newly developed techniques to avoid IVF failure.

Preimplantation Genetic diagnosis

Preimplantation genetic screening (PGS) involves the assessment of the chromosomal composition of embryos and evaluating for numerical chromosomal abnormalities with a view to selecting normal embryos for transfer. PGS should be differentiated from preimplantation genetic diagnosis (PGD). PGD allows couples where one or both partners carry a known genetic condition to have their embryos tested to avoid the transfer of a genetically affected embryo.

The application of PGD has expanded, with over 200 single gene and chromosomal disorders currently amenable to PGD. It has enabled couples affected by such disorders to avoid the need to undergo prenatal diagnosis.

What is PGD?

Preimplantation genetic diagnosis is a ray of hope for the couples with metabolic disorders, single gene disorder, X-linked disorder, translocation and severe male factor infertility. In this procedure, patients are given injections for ovarian stimulation like normal IVF (in vitro fertilization). Eggs are removed and ICSI (intracytoplasmic sperm injection) is done. Embryo biopsy can be done on day 3 or trophectoderm biopsy on day 5. The single cell is removed from the embryo and tested for various disorders.

It is preimplantation genetic testing to identify genetic defects in embryos through IVF (in vitro fertilization). Only unaffected embryos are transferred into the uterus for implantation. PGD is alternative to post conception testing like amniocentesis and chorionic villus sampling, which are difficult. It is an attractive way of preventing heritable genetic diseases

Who Should Go for PGD?

Need for PGD:

  1. The risk of implantation failure, multiple IVF failure and pregnancy loss secondary to aneuploidy increase with advanced maternal age, particularly after the age of 35 years.
  2. In theory, PGS would allow selection of normal embryos and could potentially improve implantation rates and successful outcomes with IVF.

Other Newer Techniques:

The conventional method of diagnosis of genetic defects is by a technique called PCR that is polymerase chain reaction. This is used to detect target specific whole chromosomal anomalies like Trisomy 13, 18 and 21 and sex chromosomal anomalies X and Y. It is relatively cheap and rapid to provide results within 48 hours to 72hours. Recent advances in the field of preimplantation genetic testing are,

FISH (Fluorescence In Situ Hybridization) is a useful adjunct to full conventional karyotyping when a high degree of suspicion of specific chromosome abnormality is present.

CGH (Comparative Genomic Hybridization) provides a higher detection rate of chromosomal abnormalities and more definitive diagnosis. The only drawback is the high cost.

Other newer technologies include NGS (Next Generation Sequencing). This technology allows sequencing DNA as well as RNA more quickly and can give complete genetic mapping.

To know more about preimplant genetic diagnosis, consult an infertility specialist online --> https://www.icliniq.com/ask-a-doctor-online/infertility-specialist

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Frequently Asked Questions


1.

What Diseases Can Be Detected by PGD?

Preimplantation genetic diagnosis or PGD can detect X-linked disorders, such as hemophilia, neuromuscular dystrophy, fragile X syndrome, Duchenne muscular dystrophy, and Rett syndrome. Also, single gene disorders, such as sickle cell anemia, cystic fibrosis, Huntington's disease, Tay-Sachs disease, metabolic disorders, translocation, and male factor infertility, as seen in Klinefelter syndrome and Robertsonian translocation, can be detected.

2.

How Is PGD Performed?

PGD is performed by giving injections to the patients to stimulate the ovaries, similar to an IVF (in vitro fertilization)procedure. Eggs are retrieved, and ICSI (intracytoplasmic sperm injection) is given. An embryo biopsy can be done on day three or a trophectoderm biopsy on day five. A single cell from the embryo can be tested for several disorders.

3.

Can PGD Be Performed Without IVF?

PGD (Preimplantation genetic diagnosis) cannot be performed without IVF as IVF is a requirement to obtain embryos for the purpose of PGD. In addition, PGD uses IVF so that multiple eggs can be matured and retrieved.

4.

Is PGD Harmful to the Embryo?

There may be slight chances of embryo damage. Still, there are no reports showing an increased rate of fetal malformations or any other identifiable problems in babies born with PGD IVF. However, later in life, one cannot rule out the presence of any abnormalities as a consequence of the PGD biopsy procedure.

5.

What Are the Pros and Cons of PGD?

The primary advantage of PGD includes preventing transmission of unknown genetic abnormalities with the help of early, comprehensive detection and eliminating the risk of miscarriage through improved embryo selection. The main drawback is the chances of embryo damage during the procedure.

6.

What Risks and Limitations Does PGD Have?

The limitation of this test is that, out of 23 pairs of chromosomes, only 11 pairs can be tested for PGD. The remaining 12 pairs cannot be detected. Also, the error rate for PGD in the detection of genetic abnormalities is currently known to be 10 percent. The risk associated with PGD is possible accidental damage to the embryo, although it is rare.

7.

What Percentage of Embryos Pass PGS Testing?

PGS (preimplantation genetic screening) testing has a success rate of 60 to 70 percent, meaning that if a cycle begins, eggs are retrieved, embryos are produced, PGS testing is done, and at least one embryo comes out as normal. There is a 60 to 70 percent chance of a live birth.

8.

Who Needs PGD?

PGD is required by couples with a genetic predisposition or a family history of genetic diseases. And for those with a probability of passing down a congenital abnormality, such as aneuploidy (abnormal number of chromosomes) which leads to congenital disabilities, miscarriage, or down syndrome. These can be screened with the help of PGD.

9.

Why Is PGD Controversial?

PGD is ethically controversial because of the involvement of screening and destruction of embryos for the selection of offspring based on nonmedical sex selection. Furthermore, Freeman’s argument against PGD suggests that it can lead to a disturbing tendency for eugenics, that is, the choice of specific characteristics over others.

10.

How Can You Start Your PGD Process?

You can start your PGD process by having a consultation at a fertility center to discuss the pros and cons of the procedure and why it would be best for you if you wish to go ahead. And the first step involves an IVF procedure.

Last reviewed at:
26 Aug 2022  -  3 min read

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