Genetic Testing To Prevent Birth Defects In Couples Undergoing IVF
Why doesn’t IVF treatments work for everybody? Why does a miscarriage happen? Here are the possible reasons and what can you do to increase your chances to get pregnant.
There has been an ongoing quest into deciphering the failures of infertility treatment. Why would it become ever so difficult to get pregnant and more importantly stay pregnant after a certain age?
Why do established treatments not work out for certain women? Why does a miscarriage happen? And eventually, why does a perfectly beautiful-looking embryo, not implant?
These are reasonable questions, asked by our patients but also mulled over by the clinicians and pondered over for answers by researchers alike. That brings us to the eternal quest, for knowledge! How much do we know about our embryos? A good-looking embryo is not always healthy. It may carry
1. Abnormalities in chromosome numbers where there are extra or fewer chromosomes than normal.
2. Structural rearrangements in the chromosome where a part of the chromosome detaches and is attached at the wrong location
3. Genetic mutation in a single gene, causing specific genetic or metabolic diseases
Embryos made through IVF/ICSI help us evaluate these concerns via genetic testing or Preimplantation Genetic Testing of PGT. There are different types of PGT needed for different conditions.
Preimplantation Genetic Testing- Aneuploidies (PGT-A)
PGT-A, or preimplantation genetic testing for aneuploidies, is a genetic evaluation of embryos produced through ICSI. We often wonder what leads to the failure of an IVF cycle. Patients wonder why does a cycle fail if the eggs and sperm were fertilised, formed an embryo and that embryo was placed in the uterus at an opportune time.
We know that as women age, egg reserve declines, and more and more eggs are unable to form healthy embryos. PGT-A gives information about embryos’ genetic health to help your doctor select the best embryo for transfer and improve your chance of achieving a successful pregnancy. PGT-A was formerly known as PGS, preimplantation genetic screening.
How Does It Work?
PGT-A works by looking at the right number and arrangement of chromosomes within IVF embryos. Chromosomes are extremely important for healthy growth and development as they carry the genetic code for all our growth and development.
Embryos with the incorrect number of chromosomes (also called aneuploid embryos) typically do not result in a successful pregnancy or may lead to the birth of a child with a genetic condition. Embryos with the correct number of chromosomes (also called euploid embryos) have a better chance of leading to a successful pregnancy. PGT-A identifies embryos with the correct number of chromosomes, so your care team can select the embryo with the best chance of leading to IVF success.
Preimplantation Genetic Testing- Structural Rearrangement (PGT-SR)
Sometimes parents have an inherent rearrangement of chromosomes in their bodies. This doesn’t affect them as they have all the chromosomal material. However, when the egg and sperm, divide and form an embryo, some of these rearrangements cause 25% of embryos to have an incorrect amount of genetic material. This may not be compatible with embryo growth and may cause miscarriages.
For such patients, PGT- SR can diagnose the normal and abnormal embryos and help select the normal ones to be preferred for placing back inside the womb.
Preimplantation Genetic Testing- Monogenic Disorders (PGT-M)
Many families carry some defective genes that can give rise to known genetic disorders. Some of these are incompatible with healthy life if inherited from one or both parents. These are called Single Gene Disorders. Here, a single known gene is responsible for the continued disorder in the offspring of a family line.
Earlier the only way to diagnose this was to test the foetus in utero and if the foetus was found to carry the defect, terminate the pregnancy. This is an especially stressful and disturbing event for a couple and especially for the expecting mother. It may also not always be safe to terminate a pregnancy. In such a scenario, PGT- M comes as a boon to those who wish to take steps before a pregnancy is established in the uterus.
IVF/ ICSI helps us to make the embryos outside the human body. These embryos can then be tested by a procedure called embryo biopsy to locate the defective gene. Few cells from an embryo made out of In Vitro Fertilisation are removed by a very fine and skilled procedure. This does not affect the embryo itself. The embryo is then frozen and kept secure while the cells extracted are sent for a special analysis for the defective gene.
Finding The Perfect Gene Is Important
Looking for the gene is like looking for a needle in the haystack. A human body has 23 pairs of chromosomes, each made out of many genes. These genes regulate entire beings and the functions of the human body. It’s estimated there are around 20,000-25,000 gene pairs in a human body. However, each gene can be isolated by a specific probe, that binds to a particular gene.
While looking for a single defective gene in an embryo, this probe is prepared based on information from the genetic mutation test of the parents and affected family members. Then the IVF resultant embryo biopsy cells are tested with the probe. Once it’s identified that a particular embryo doesn’t have the defect, it is selected for implantation back in the womb of the intending mother. As well known, each embryo transfer will give a realistic chance of pregnancy. It’s not an assurance to pregnancy. However, it’s an assurance that the given defect is not carried in the implanted embryo and hence the pregnancy will be healthy.
Many couples with carrier genes of diseases like Thalassemia, Muscular Dystrophy, Polycystic kidneys, and metabolic disorders like Methylmalonic acidemia, carriers of the BRCA gene implicated in breast cancer, etc are now approaching us to help conceive healthy offspring.
PGT-M gives an option to these couples to check their embryos before implantation and avoid the trauma of termination of pregnancy. The concerns over abnormal offspring after IVF stems mainly from the advanced age of women opting for IVF as a population group and not due to the actual process of IVF. Genetic testing would reduce the chances of Genetic abnormalities in offspring when judiciously offered. Overall, Genetic testing has opened up a new arena of scientific information and assessment of human embryos helping people to prevent genetic disorders, congenital defects, and recurrent miscarriage!
(This article is contributed by Dr Richa Jagtap, Clinical Director, Consultant Reproductive Medicine, Nova IVF Fertility, Mumbai)
