An Overview
Preimplantation genetic testing refers to a group of laboratory techniques used to examine the genetic makeup of embryos created through IVF before any embryo is transferred to the uterus. The purpose is to identify embryos with the greatest likelihood of producing a healthy pregnancy, and to avoid transferring embryos affected by specific genetic conditions.
The technique has advanced considerably over the past decade. Earlier methods examined a small number of chromosomes on day-three embryos; contemporary practice involves a biopsy of a few cells from the trophectoderm — the outer layer that will become the placenta — at the blastocyst stage on day five or six, followed by next-generation sequencing. This approach is more accurate and less disruptive to the developing embryo.
The Three Categories
PGT-A, testing for aneuploidy, screens embryos for an abnormal number of chromosomes. Aneuploidy is the single most common cause of implantation failure and early miscarriage, and its frequency rises sharply with maternal age. In women over 40, a majority of embryos may be aneuploid despite appearing morphologically normal under the microscope.
PGT-M, testing for monogenic disorders, is used when both parents are known carriers of a single-gene condition. In the United Arab Emirates, where consanguineous marriage remains common in some communities, this application is particularly relevant for conditions such as beta-thalassaemia, sickle cell disease, cystic fibrosis, and spinal muscular atrophy.
PGT-SR, testing for structural rearrangements, is offered to couples where one partner carries a balanced chromosomal translocation or inversion. Such carriers are usually healthy themselves but produce a high proportion of unbalanced embryos, which explains recurrent miscarriage in many of these couples.
Who Should Consider It
PGT is not required for every patient. It is most clearly beneficial for women of advanced reproductive age, couples with recurrent pregnancy loss, those who have experienced repeated implantation failure despite good-quality embryo transfers, and couples with a known genetic condition or a previously affected child.
For young patients with a good prognosis and few embryos, the calculus is different. Testing carries a laboratory cost, requires embryos to reach the blastocyst stage, and involves a biopsy. Where only one or two embryos are available, testing may not change management. These decisions should be made in consultation with a fertility specialist and, where a specific genetic condition is involved, a clinical geneticist.
The Process
A PGT cycle follows the standard IVF pathway of ovarian stimulation, egg retrieval, and fertilisation, usually by ICSI to avoid contamination from residual sperm DNA. Embryos are cultured to the blastocyst stage, biopsied, and then vitrified while the genetic analysis is performed, which typically takes one to two weeks.
Results classify each embryo as euploid, aneuploid, or mosaic. Euploid embryos are prioritised for transfer in a subsequent frozen embryo transfer cycle. Mosaic embryos — those showing a mixture of normal and abnormal cells — require careful counselling, as some have resulted in healthy live births, and management depends on the specific chromosomes involved.
Benefits and Limitations
The principal benefits are a reduced risk of miscarriage, fewer failed transfers, a shorter time to pregnancy in appropriately selected patients, and the ability to transfer a single embryo with confidence, thereby avoiding the maternal and neonatal risks of twin pregnancy.
It is equally important to understand what PGT does not do. It does not create better embryos; it selects among those already produced. It cannot improve the outcome for a patient whose embryos are all abnormal, and it does not test for every genetic condition. A small false-positive and false-negative rate exists, and confirmatory prenatal testing during pregnancy remains recommended.
A Considered Decision
PGT is a valuable tool when applied to the right patients for the right reasons. The decision should follow a detailed discussion of a couple’s history, age, embryo numbers, and specific genetic risks, alongside a clear explanation of costs and expected benefit.
At New Hope IVF Hospital, Sharjah, our embryology laboratory and clinical team provide genetic counselling and PGT services in line with international standards and UAE regulatory requirements, ensuring that each couple’s decision is fully informed.