Fertility Treatments

Genetic Testing pgd & pgs

It is a diagnostic process through which the doctors analyse a person’s chromosomes or DNA for traits for interesting DNA sequences.

Introduction

Genetic testing is a diagnostic process through which the doctors analyse a person’s chromosomes or DNA for traits for interesting DNA sequences. The process aims to identify the genetic mutations that may be causing a particular illness or maybe a reason behind the individual being afflicted with an inherited disease, arising spontaneously. Nowadays, there are some companies offering home genetic testing kits. With these kits, you can efficiently perform a genetic test on yourself via ear wax, cheek swab, etc., to find out your ancestry as well as the presence of a congenital medical condition. 

Moreover, you may opt to take a genetic test before you are looking to start a family in order to determine your status as a carrier of certain hereditary medical conditions, such as cystic fibrosis. 

Suppose you are looking to go for an artificial reproductive technique like IVF for child conception. In that case, the doctor may advise you to have genetic testing for your fertilised embryos before implantation. Doctors usually perform two tests on the embryos, preimplantation genetic screening or PGS and preimplantation genetic diagnosis or PGD. After these tests, the doctor will implant the embryos that don’t contain any presence of an illness, congenital abnormalities, contamination, etc., into the female partner’s uterus.

What Is PGD?

PGD or preimplantation genetic diagnosis is genetic testing aimed at detecting genes associated with a few particular diseases. For example, suppose you or your partner have a family history of a specific hereditary disease. In that case, the PGD test can help you ensure that your forthcoming child, being born via IVF or any other artificial reproductive technique, won’t be born with that disease. However, you or your partner suffering from a particular illness is not necessarily a criterion for performing this test. In several cases worldwide, a parent may not suffer from a disease but still be a carrier of it. 

Here are a few diseases detected in the embryo with the help of PGD:

  • Marfan syndrome
  • Haemophilia
  • Huntington’s disease
  • Duchenne Muscular Dystrophy
  • Cystic fibrosis
  • An abnormal number of chromosomes
  • Mental retardation, congenital disabilities and even miscarriage due to the exchange of chromosomal material. 

 

If you are looking to have a child through IVF (or other ARTs), you may want to consider having a PGD on your embryos to have a successful pregnancy.

What Is PGS?

PGS, or preimplantation genetic screening, is a genetic testing process to determine the number of chromosomes in your embryo cells. Usually, in perfect health, you will have 23 pairs of chromosomes. Although IVF possesses a risk of multiple pregnancies, the doctor will place 2 or 3 embryos in your uterus to ensure a successful pregnancy. However, suppose the doctor conducts a PGS test right after the fertilisation before implantation. In that case, they’ll most likely place the healthiest embryo to ensure a successful pregnancy without the risk of multiple births. That is because an embryo having a chromosome more or less than usual will most likely fail to latch on to the uterine lining properly and result in miscarriage.

Moreover, increasing age increases the risk of an abnormal number of chromosomes in her embryos. That’s why preimplantation genetic screening is recommended for women over 35 looking to start a family through in vitro fertilisation. You may also try it if you’ve had multiple miscarriages. 

Unlike PGD, PGS is not performed for identifying particular diseases. Also, it is much simpler of a process than PGD. But it may help you detect down syndrome because it is caused due to an extra chromosome, Trisomy 21, in an individual’s DNA. You may also opt for gender selection. 

PGS can help you identify some chromosomal abnormalities, including: 

  • One segment of a chromosome is rearranged or translocated into another chromosome.
  • Deletion or duplication of X and Y chromosomes, and other sex-chromosome abnormalities like Turner Syndrome and Klinefelter Syndrome. 
  • Aneuploid – the presence of an incorrect number of chromosomes in a cell, like having 45 or 47 chromosomes instead of the usual 46. 
  • Deleted or missing chromosomal segment.

 

Preimplantation genetic diagnosis and preimplantation genetic screening are not necessary for the IVF process. That’s why the cost of IVF doesn’t usually include these testing processes. Instead, a sample of amniotic fluid is taken after embryo culture for testing in both PGD and PGS. The embryo’s health is at risk while taking the sample. If any harm is inflicted upon the embryo, the pregnancy will most likely be unsuccessful. 

Moreover, since 5 to 6 embryo samples are required for PGS, it tends to be an issue for older women, as they usually are not able to produce that many embryos in a single IVF cycle. That’s why they’ll require two or more IVF cycles just to produce enough embryos. For more information or to undergo the procedure, you may want to visit Siya Health, as our doctors can identify the need for PGD or PGS and perform them successfully.

How Do These Tests Work?

First off, the doctor will remove one or more cells from the embryo while growing in the fertility lab. The testing stages will be different for different techniques, including microarray, FISH or fluorescent in situ hybridisation and single-nucleotide polymorphism or SNP. The embryo cells will then be tested for a gene causing a particular disease. Finally, the doctor will determine if your embryo is afflicted with an illness and if that disease affects the embryo. 

Although you may not have the signs and symptoms of a particular disease, you may still pass it on to your offspring as a carrier.

PGS

The method for screening all 24 chromosomes is known as CCS or comprehensive chromosomal screening. The most common CCS techniques are: 

  • aCGH or array-comparative genomic hybridisation
  • NGS or next-generation sequencing (NGS may soon replace aCGH due to a higher resolution by examining more data points)

 

These techniques are performed on the embryos during day 5 or 6, also known as the blastocyst stage, or less often, on a few cells of the embryo on day 3.

PGD

Traditionally, in preimplantation genetic diagnosis, the DNA probe will be custom made for a particular genetic mutation in an individual. In addition, a blood sample or buccal smear will have to be obtained if a person is thinking of going for IVF with PGD. The process of development of customised tests will take around 12 to 16 weeks. 

But nowadays, there is a new PGD method called karyomapping, which takes just around a few weeks for test development and allows testing any kind of genetic mutation. Simply put, this technique tests the embryos for finding the fingerprint associated with the chromosome carrying the defective gene. So if it finds an embryo with that particular fingerprint, it would mean that the embryo has inherited the defective gene-carrying chromosome. 

Often, PGD is carried out with PGS to select an embryo with a specific number of chromosomes without any known genetic mutation. 

Then, a karyotype, a genetic test for checking the chromosomes, is performed during pregnancy via amniocentesis or a chorionic villus sampling. It can determine if a fetus has an odd number of chromosomes (more or less than 46), as it may cause down syndrome. It can also look for chromosomal translocations, which may result in issues with development and growth.

Should You Consider PGS Or PGD?

PGS is considered to be better than the visual microscopic observation (often used in IVF), as it analyses the embryos for any chromosomal abnormalities and the normal chromosomal make-up with better precision. That’s why PGS helps the doctor identify and implant the healthiest embryos to increase the probability of a successful pregnancy. 

You, as a couple, will be suitable for PGS if you are at an increased risk of having chromosomal abnormalities. Here are a few other candidates who may want to opt for PGS:

  • Have had multiple miscarriages
  • The female partner is over 35
  • Have had failed IVF attempts

 

You may also undergo preimplantation genetic screening if you want a single embryo transfer to prevent multiple births, desire the healthiest baby through IVF or want family balancing. 

PGD is also an excellent genetic testing technique, as it allows the doctor to select an embryo without any genetic mutation, congenital abnormalities, contamination, etc., for implantation. You may choose PGD for any medical condition for which there is an exact mutation. 

PGD is quite suitable if:

  • You have chromosomal translocation or rearrangement (if a particular chromosome is not in its specific position).
  • You want to match stem cells if one or more of your family members require a tissue donor.
  • You have an illness like cystic disease, cystic fibrosis, Tay Sachs disease.
  • You have a child suffering from a congenital disease due to genetic mutation.

 

Several factors would determine whether or not a couple looking for IVF should undergo both PGD and PGS.

What Are The Chances Of Conceiving A Baby?

With PGS, the success of the IVF will depend on the number of healthy embryos produced during the IVF cycle. According to current statistics, there is a 60% to 80% chance of a single frozen embryo turning into a live birth. This data is considered excellent since most women undergoing IVF with PGS tend to produce chromosomally irregular embryos, are at an advanced maternal age, have had miscarriages, and even multiple failed IVF attempts.

But, there is a possibility that none of your embryos is suitable for transfer to the uterus. The reasons for that are:

  • Damage to the embryos while taking the cell sample for genetic testing
  • Insufficient embryos
  • All embryos are aneuploids

 

When it comes to PGD, there is not enough data to claim whether or not it is successful. But most couples opting for this testing technique aren’t really suffering from infertility. Instead, they want to ensure that there is little to no risk of genetic disease in their forthcoming child.

But there is a chance that there are no embryos for transferring to the uterus in case there are insufficient eggs, taking a cell sample has damaged the embryos, or all embryos suffer from a congenital disease.

Is a prenatal test necessary after genetic testing?

PGD and PGS tests cannot be claimed as 100% accurate since they are conducted on a very tiny piece of tissue. That’s why the doctors recommend undergoing prenatal testing to confirm the normal chromosomal make-up in the fetus. Since they collect more cells from the fetus for testing, CVS and amniocentesis are considered to be more accurate.

Conclusion

Genetic testing is considered to be quite beneficial as it can test for diseases like Huntington’s disease, Tay-Sachs disease, breast cancer, Fragile-X syndrome, etc. 

PGS, or preimplantation genetic screening, is a genetic testing process to determine the number of chromosomes in your embryo cells. Although PGS is not performed for identifying particular diseases, it may help you diagnose Down syndrome as it is caused due to an extra chromosome, Trisomy 21, in an individual’s DNA. 

Suppose you or your partner have a family history of a particular hereditary disease. In that case, the PGD test can help you ensure that your forthcoming child, being born via IVF or any other artificial reproductive technique, won’t be born with that disease.

If you are an older woman who has had multiple failed IVF attempts and miscarriages, you may want to undergo PGS. But if you are worried about your forthcoming child being born with a genetic disease, PGD will help.

So get in touch with the experts at Siya Health if you want to undergo PGD or PGS. Our experts aim at making your pregnancy as successful as possible.

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Dr. Dipesh Sorathiya

M.S. (Obs & Gyn)
DIP. in Gynec Endoscopy (CICE)

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