Preimplantation genetic testing is one of the most significant advances in IVF medicine of the past two decades. The ability to analyse the chromosomal and genetic composition of an embryo before it is transferred into the uterus has fundamentally changed how fertility specialists approach embryo selection, and it has offered new hope to specific groups of patients for whom previous IVF outcomes were consistently poor.
Yet for many patients encountering these terms for the first time, the language of genetic testing in IVF is confusing. PGT-A, PGT-M, PGT-SR. Aneuploidy, monogenic disease, structural rearrangements. Biopsy, vitrification, euploid. The concepts are not inherently complicated, but they are rarely explained clearly in the rushed context of a fertility consultation.
This guide explains each type of preimplantation genetic testing in plain language, who benefits from each, what the process involves, and what the evidence says about the impact on IVF outcomes.
What Preimplantation Genetic Testing Actually Is
Preimplantation genetic testing refers to the analysis of genetic material from an embryo created through IVF before that embryo is transferred into the uterus. The testing is performed on cells biopsied from the embryo at the blastocyst stage, typically on day five or six of development, before the embryo is frozen and the biopsy sample is sent to a specialist genetics laboratory for analysis.
The goal of testing depends on what is being looked for. Some testing focuses on chromosomal number, identifying whether the embryo has the correct 46 chromosomes. Other testing looks for specific inherited genetic conditions carried by one or both parents. Each type of testing addresses a different clinical question and is appropriate for different patient populations.
It is important to understand that preimplantation genetic testing does not guarantee a successful pregnancy. It significantly improves the selection of embryos with a higher probability of implanting successfully and developing into a healthy baby, but it does not eliminate all sources of IVF failure or all risk of genetic conditions in the resulting child. It is a powerful tool for improving odds, not a certainty of outcome.
PGT-A: Testing for Chromosomal Abnormalities
PGT-A, preimplantation genetic testing for aneuploidy, is the most widely used form of embryo genetic testing in IVF globally. Aneuploidy refers to an abnormal number of chromosomes, and aneuploid embryos are the single most common cause of IVF implantation failure and early miscarriage.
A human embryo should contain 46 chromosomes in 23 pairs. An aneuploid embryo has too many or too few chromosomes due to errors in cell division during egg or sperm maturation. Most aneuploid embryos either fail to implant, cause a very early pregnancy loss, or result in miscarriage. A small proportion develop further but result in chromosomal conditions such as trisomy 21, trisomy 18, or monosomy X.
PGT-A identifies which embryos in a cohort are euploid, meaning chromosomally normal, and which are aneuploid. Only euploid embryos are selected for transfer, which improves the implantation rate per transfer, reduces miscarriage rates, and in some studies improves cumulative live birth rates compared to transferring untested embryos.
The patients who benefit most from PGT-A include women over 35 where the proportion of aneuploid embryos increases significantly with age, couples with a history of recurrent miscarriage where chromosomal abnormality in embryos is a likely contributing factor, couples with repeated IVF implantation failure despite good embryo quality, and couples who have previously had a pregnancy affected by chromosomal abnormality.
PGT-A is not universally recommended for all IVF patients. In younger women with good ovarian reserve and no history of miscarriage or implantation failure, the evidence for routine PGT-A is less compelling, partly because the proportion of aneuploid embryos is lower and partly because the biopsy process and the reduction in available embryos for transfer must be weighed against the selective benefit.
The biopsy procedure itself is performed by a skilled embryologist who uses a laser to create a small opening in the trophectoderm and removes five to ten cells using a fine glass pipette. The embryo is immediately vitrified following biopsy while the cells are analysed, and results are typically available within one to two weeks. Only euploid embryos are subsequently warmed and transferred in a frozen embryo transfer cycle.
PGT-M: Testing for Inherited Single Gene Conditions
PGT-M, preimplantation genetic testing for monogenic disorders, is performed when one or both parents carry a known genetic mutation that causes a specific inherited condition and wish to avoid passing that condition to their child.
Single gene disorders that can be tested for through PGT-M include cystic fibrosis, spinal muscular atrophy, Huntington's disease, sickle cell disease, thalassaemia, fragile X syndrome, BRCA1 and BRCA2 mutations associated with hereditary breast and ovarian cancer, and a wide range of other heritable conditions depending on the specific mutation identified in the family.
PGT-M is technically more complex than PGT-A because it requires the development of a bespoke test for the specific genetic mutation carried by the couple before the IVF cycle begins. This preparation phase, sometimes called workup, involves analysing DNA samples from both partners and often from affected family members to design a test that can reliably identify whether an embryo has inherited the mutation in question. This workup typically takes several weeks to complete and must be organised before the stimulation cycle begins.
Once the bespoke test is ready, the IVF cycle proceeds as normal. Embryo biopsy is performed at the blastocyst stage and the biopsied cells are analysed using the pre-designed test. Embryos identified as unaffected by the genetic mutation are available for transfer, while those carrying the mutation can be excluded. In many cases PGT-M is performed simultaneously with PGT-A, allowing both chromosomal normality and mutation status to be confirmed before transfer.
PGT-M is appropriate for couples who are known carriers of a serious heritable condition and wish to avoid having an affected child without resorting to prenatal diagnosis and the decision about termination that a positive result would require. It allows selection of unaffected embryos before pregnancy begins, providing a proactive rather than reactive approach to inherited disease prevention.
PGT-SR: Testing for Structural Chromosomal Rearrangements
PGT-SR, preimplantation genetic testing for structural rearrangements, is used when one partner carries a balanced chromosomal rearrangement such as a translocation or inversion. Balanced carriers have the correct total amount of genetic material but it is arranged differently than usual, with segments of chromosomes in different positions or orientations than normal.
Balanced carriers are typically healthy themselves because all their genetic material is present, just rearranged. However, during the production of eggs or sperm, the rearrangement can result in gametes with unbalanced chromosomal complements, meaning too much or too little of specific chromosomal regions. Embryos created from these unbalanced gametes carry chromosomal imbalances that typically result in miscarriage or, if the pregnancy continues, significant developmental abnormalities.
Couples where one partner is a known translocation carrier have significantly elevated rates of miscarriage and IVF failure due to the high proportion of unbalanced embryos produced. PGT-SR analyses embryo biopsy samples specifically to identify whether the embryo carries a balanced or normal chromosomal arrangement, allowing only balanced or normal embryos to be selected for transfer.
The clinical benefit of PGT-SR in translocation carriers is substantial and well-established. Studies have found dramatic reductions in miscarriage rates and significant improvements in live birth rates per transfer in couples using PGT-SR compared to transferring untested embryos. It is one of the most clearly indicated applications of preimplantation genetic testing in reproductive medicine.
What to Expect From the Genetic Testing Process
The logistics of genetic testing in IVF require some additional planning and patience compared to a standard cycle without testing. The biopsy, vitrification, testing, and awaiting of results adds a period of several days to several weeks to the overall cycle timeline depending on the type of testing and the turnaround time of the genetics laboratory used.
For PGT-A, results typically return within one to two weeks of biopsy, after which a frozen embryo transfer is scheduled in a subsequent cycle. For PGT-M, the preparation workup before the cycle begins adds several weeks to the overall timeline, though the biopsy and results process is comparable to PGT-A once the cycle is underway.
Not all embryos biopsied will return a result. A small proportion of biopsy samples do not contain sufficient DNA for analysis or produce an inconclusive result due to technical limitations. These embryos may be re-biopsied in some circumstances or may need to be excluded from the available embryo pool.
Patients should also be prepared for the possibility that testing reveals fewer transferable embryos than anticipated. Learning that a carefully developed blastocyst is aneuploid or carries a genetic mutation is emotionally difficult, and having support in place for this possibility is part of responsible pre-cycle preparation.
Consulting an experienced best ivf doctor in jaipur who has specific expertise in preimplantation genetic testing protocols, works with a high-quality genetics laboratory, and provides thorough pre-testing counselling ensures that your decision to pursue genetic testing is based on accurate information and that the process is managed with the clinical precision it requires.
Final Thoughts
Preimplantation genetic testing has transformed outcomes for specific groups of IVF patients and continues to evolve as the technology improves and our understanding of embryo genetics deepens. For the right patients, it offers a meaningful improvement in the probability of a successful pregnancy and a significant reduction in the risk of miscarriage and inherited genetic disease.
For every patient considering it, thorough counselling, honest discussion of its limitations, and individualized assessment of whether it is appropriate for their specific situation are essential before the decision is made.
A dedicated best ivf hospital in jaipur with advanced genetic testing capabilities, experienced reproductive specialists, and access to specialist genetics laboratory partnerships provides the comprehensive clinical infrastructure that evidence-based preimplantation genetic testing requires.
