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What is Preimplantation Genetic Diagnosis?

One of the most rewarding experiences of any couple’s life is parenthood. However, parenthood comes with a slew of new duties for both parents. It is also accompanied by a tremendous deal of worry and anxiety about the baby’s health — whether the fetus is under stress, whether there are chances of complications developing during delivery, if the child will be born with potential genetic disorders, and so on.. 

For Jennifer (a 33-year-old freelance film editor from the United States), these pressing doubts were resolved by Preimplantation genetic testing.

Jennifer and her partner decided to visit a doctor right after conceiving to enquire about the chances of their child being born with haemophilia. Jennifer’s father had haemophilia, and she was pretty sure she was a carrier of this X-linked disease. As someone who knew the hardships of growing up with haemophilia, she wanted to be clear about it right from the beginning. 

Since it was early days in her pregnancy, the gynaecologist recommended Preimplantation Genetic Diagnosis. Jennifer agreed as it was a safer choice than the other recommended method of amniocentesis, which can cause trouble to the foetus and is performed during the later stages of the pregnancy.

The results stated that the baby would not be a haemophiliac but would continue to carry the gene for it, thereby mitigating Jennifer’s restlessness. 

What is Preimplantation Genetic Diagnosis?

Preimplantation genetic testing is a technique for detecting genetic problems in in-vitro fertilisation (IVF) embryos before they are implanted. When one or both genetic parents have a known genetic condition, preimplantation genetic diagnosis (PGD) is used to describe the process of testing an embryo to check if it, too, has a genetic fault. 

Preimplantation genetic screening (PGS), on the other hand, refers to approaches for detecting aneuploidy in embryos from defects in genes of parents that are assumed to have normal chromosomes.

Preimplantation genetic testing is an alternative to conventional preconception diagnostic techniques (such as amniocentesis or chorionic villus sampling), which are frequently followed by the challenging option of terminating a pregnancy if the results are unfavourable. 

Currently, PGD and PGS are the only methods for preventing a high chance of having a child with a genetic condition before implantation. 

The following section explains every detail of this method of prenatal diagnosis. 

What are the types of Preimplantation Genetic Diagnosis?

In PGT, two types of testing solutions are usually employed to determine an embryo’s condition. A single sample can now be utilised for both PGT-A and PGT-M IVF research within a straightforward, integrated process thanks to the capability of Ion Torrent NGS technology.

Preimplantation genetic testing-aneuploidy (PGT-A):

  • Aneuploidies, or chromosomal abnormalities, are detected across all 24 chromosomes using this test (22 autosomes and the X and Y chromosomes)
  • Trisomy 21 (Down syndrome) and monosomy X are two examples (Turner syndrome)

Preimplantation genetic testing-monogenic (PGT-M):

  • Within a family, linkage analysis identifies important alleles for single-gene diseases.
  • Sickle cell anaemia, cystic fibrosis, Huntington disease, fragile-X syndrome, and spinal muscular dystrophy are only a few examples. The doctors suggested this method of monogenic Preimplantation genetic testing to Jennifer.

Who should go for Preimplantation Genetic Diagnosis?

The following potential candidates for a preimplantation genetic test:

  • Couples having a history of X-linked illnesses in their family (Couples with an X-linked disease in their family have a 25% chance of having an afflicted embryo [half of the male embryos].)
  • Couples with chromosomal translocations, which can result in implantation failure, recurrent pregnancy loss, or offspring with mental or physical abnormalities [4].
  • Autosomal recessive disease carriers (Carriers of autosomal recessive illnesses have a 25% chance of having an embryo afflicted.)
  • Autosomal dominant disease carriers (Carriers of autosomal dominant illness have a 50% chance of having an embryo afflicted.

Conditions diagnosed by Preimplantation Genetic Diagnosis

  • Sex-linked disorders
  • Single gene defects
  • Chromosomal disorders

How to infer if one should go for PGD or not?

Consulting a doctor is the best way to confirm. Still, the cases can be broadly generalised as:

  • Women who are nearing the end of their pregnancy
  • Couples who have had previous miscarriages
  • Couples who have had many IVF failures
  • Severe male factor infertility in the male spouse

When is Preimplantation Genetic Diagnosis done?

Testing the early embryo following in-vitro fertilisation is known as a preimplantation genetic diagnosis. At the 6-10 cell stage (day 3 of development), one or two cells (blastomeres) are removed from the preimplantation embryo during the biopsy, allowing intact embryos to be implanted into the uterus.

How long does it take to deliver results?

The majority of tests are returned in two to three weeks. However, some may take up to eight weeks. During your meeting, your genetic counsellor will go over this with you. Jennifer received the results a month later, as the clinic had an extreme workload. 

If you’ve just conceived and your mind is flooded with questions and doubts, firstly, know that your concerns and questions are justified. As any responsible parent, it is your right to learn every last detail about your future child before their birth.

So, take a deep breath and go in for the critical preimplantation genetic diagnosis to put your mind at ease.

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