Genetic Testing (PGT) in Chennai

Preimplantation Genetic Testing (PGT) is the genetic screening of embryos created during an IVF cycle, carried out before any embryo is transferred to the uterus. A few cells are removed from each embryo and analysed, so that the embryo selected for transfer is one already known to be genetically normal.

The reason this matters is that chromosomal abnormality in the embryo is the single most common cause of IVF failure and of early miscarriage. An embryo can look perfect under the microscope, well-formed, dividing on schedule, graded highly by an embryologist, and still carry the wrong number of chromosomes. Such an embryo will usually fail to implant, or will implant and then miscarry. Appearance alone cannot detect this; only genetic testing can.

The proportion of embryos affected rises sharply with maternal age, which is why PGT is most often discussed with women over 35, with couples who have had repeated IVF failure, and with couples who have suffered recurrent pregnancy loss.

PGT is not one test but three, used for different purposes: PGT-A for chromosome number, PGT-M for a specific inherited single-gene disorder, and PGT-SR for structural chromosomal rearrangements. They are explained below, because choosing the right one depends entirely on what you are trying to find.

PGT is always performed within an IVF cycle. It cannot be done in natural conception, because there is no embryo outside the body to test.

These three tests share a technique but answer entirely different questions. Choosing between them is not a matter of preference: it depends on what, specifically, you have reason to look for.

PGT-A (Aneuploidy) counts chromosomes. A normal embryo has 46; an aneuploid embryo has too many or too few, and most such embryos either fail to implant or miscarry. Some, such as an extra chromosome 21, result in a live birth with a chromosomal condition: in that case, Down syndrome. PGT-A does not look for any particular inherited disease; it simply checks that the count is right. This is the test used when the concern is age-related chromosomal risk, repeated IVF failure, or recurrent miscarriage, and it is by far the most commonly performed.

PGT-M (Monogenic) looks for one specific single-gene disorder that the parents are known to carry: thalassemia, cystic fibrosis, sickle cell disease, spinal muscular atrophy and others. It is not a screen. It is a targeted search for a known mutation in a family, and it can only be performed when that mutation has already been identified through prior genetic testing of the parents. For carrier couples who face a recurring risk of passing on a serious inherited condition, PGT-M is the reason to consider IVF even when fertility is otherwise normal.

PGT-SR (Structural Rearrangements) is for people who carry a balanced chromosomal rearrangement, such as a translocation or inversion. A carrier is typically healthy, all the genetic material is present, just arranged differently, but the embryos they produce can inherit an unbalanced amount of it, causing miscarriage or a child with serious abnormalities. PGT-SR identifies the embryos that have inherited a balanced or normal arrangement.

Getting this right is precisely why genetic counselling comes before treatment, not after. The counselling session determines which test is appropriate, whether it is appropriate at all, and what it can and cannot tell you.

PGT adds cost and complexity to an IVF cycle, and it is not right for everyone. Being honest about who benefits is more useful than presenting it as a universal upgrade.

PGT is most clearly worthwhile when:

• You carry a known single-gene disorder or a chromosomal rearrangement and want to avoid passing it on. Here the case is strongest, and PGT is often the entire reason for doing IVF.
• You have had recurrent pregnancy loss, where chromosomal abnormality in the embryo is a leading cause.
• You have had repeated IVF failure with good-quality embryos that did not implant.
• You are over 35, and particularly over 38, where the proportion of chromosomally abnormal embryos rises steeply.
• A previous pregnancy was affected by a chromosomal condition.

PGT is less likely to help when: you are young, have a good ovarian reserve, and are producing several good-quality embryos in your first cycle. In that situation many of your embryos are likely to be normal anyway, and testing adds cost, a biopsy, and a delay: while the embryo you would have transferred first may well have been the one PGT would have chosen.

There is also an uncomfortable scenario to acknowledge: if you produce only one or two embryos and testing shows them to be abnormal, you will have no embryo to transfer at all. The information is real and it is worth having: but it can end a cycle that would otherwise have proceeded in hope. That is a trade-off you should make knowingly rather than discover afterwards.

Dr. Rukkayal will tell you honestly whether PGT is likely to help in your specific case, rather than recommending it by default.

The concern almost every couple raises is the obvious one: you are taking cells out of my embryo: will that harm the baby? It is the right question, and the answer depends on when and where the cells are taken.

The biopsy is performed at the blastocyst stage, on day 5 or 6 of embryo development. By this point the embryo has already differentiated into two distinct parts: an inner cell mass, which goes on to become the baby, and an outer layer called the trophectoderm, which goes on to become the placenta.

The biopsy takes a few cells from the trophectoderm, the future placenta, and does not touch the inner cell mass. This is the entire basis of its safety, and it is why the timing matters so much. Biopsy at this stage is well established, and studies have not shown an increased risk of birth defects.

Because results take two to three weeks to come back, the embryos are vitrified (flash-frozen) while testing proceeds. The transfer therefore happens in a later frozen embryo transfer cycle rather than fresh. This is not a drawback: frozen transfer also allows the uterine lining to be prepared optimally, without the hormonal effects of a stimulation cycle.

Two limitations should be stated. The biopsy samples a handful of cells, not the whole embryo, and in rare cases an embryo can contain a mix of normal and abnormal cells (mosaicism), which can make a result ambiguous. And no genetic test is 100% accurate: PGT dramatically reduces risk, but it does not reduce it to zero, and it is not a substitute for the antenatal screening you would have in any pregnancy.

PGT is frequently oversold, and it is worth being precise about its boundaries.

What PGT can do: identify embryos with the wrong number of chromosomes; identify embryos carrying a specific single-gene disorder that you are known to carry; identify embryos that have inherited an unbalanced chromosomal rearrangement; and thereby improve the chance that the embryo transferred will implant and result in a healthy live birth, while reducing the risk of miscarriage. That is a substantial and genuine benefit, and it is reflected in the success rates on this page.

What PGT cannot do:

• It cannot create good embryos. It selects among the embryos you have. If all of them are abnormal, PGT reports that fact: it does not change it. This is the most common misunderstanding, and the most important one.
• It cannot screen for every genetic condition. PGT-M looks for one known mutation, not for all possible disease. There is no test that screens an embryo for everything.
• It cannot guarantee a healthy baby. Many conditions are not chromosomal or single-gene in origin, and no embryo test can exclude them.
• It cannot overcome age. PGT identifies the normal embryos of a 42-year-old; it does not make her embryos those of a 30-year-old. If very few normal embryos exist, that is what the test will find.

Understood correctly, PGT is a selection tool, not a creation tool. It helps you transfer the best embryo you have. It cannot give you a better one than you have.