Preimplantation Genetic Testing (PGT) is an advanced laboratory procedure performed during IVF to analyze embryos for genetic abnormalities before they are transferred to the uterus. It functions as a detailed genetic screening that helps identify embryos with the highest likelihood of resulting in a healthy pregnancy. PGT does not change the number of viable embryos created, but rather helps guide embryo selection based on genetic information. PGT is performed after embryos are created through IVF. On day 5 or 6 of development, when embryos reach the blastocyst stage, a small number of cells are carefully biopsied by experienced embryologists. These cells are analyzed in a specialized laboratory, while the embryos themselves are safely vitrified and stored. Once results are available—typically within 7–14 days—embryos deemed suitable based on the specific type of testing performed are selected for transfer in a subsequent cycle. There are different types of PGT, each designed to evaluate specific genetic risks. PGT-A (Preimplantation Genetic Testing for Aneuploidy) screens embryos for abnormalities in chromosome number and is most commonly recommended for patients of advanced maternal age or those with recurrent miscarriage, as chromosomal abnormalities increase with age. Other forms of PGT, such as PGT-M, may be recommended when both partners are carriers of the same inherited genetic condition, helping prevent transmission of serious genetic diseases. PGT is not mandatory for all IVF patients, and its benefits depend on individual circumstances. It is most strongly recommended for patients with age-related risk factors, a history of pregnancy loss, repeated implantation failure, or known genetic concerns identified through carrier screening. In contrast, younger patients under 35 with no history of miscarriage or genetic issues often have a high proportion of chromosomally normal embryos and may see less benefit from routine testing. There are also situations where PGT may not be ideal. Patients who produce a limited number of embryos may find testing less practical, as embryo biopsy—while generally safe—carries a small risk. Financial considerations are also important, as PGT adds cost and time to IVF treatment and typically requires frozen embryo transfer rather than a fresh transfer. Clinical evidence supports the use of PGT-A in appropriately selected patients. A large study by Munné et al. (2019) demonstrated that PGT-A can reduce miscarriage rates and improve live birth rates per embryo transfer, particularly in women over 35. However, PGT cannot guarantee a healthy baby, as it does not detect all possible genetic or developmental conditions. When performed by experienced embryology teams, embryo biopsy is considered safe and has not been associated with increased risks of birth defects or developmental problems. If testing reveals that all embryos are genetically abnormal, fertility specialists work closely with patients to discuss next steps, which may include additional IVF cycles, donor eggs, or alternative family-building options. PGT can also be performed on embryos that were frozen during a previous IVF cycle. In these cases, embryos are thawed, biopsied, and refrozen prior to transfer. While this involves additional handling, it allows patients to benefit from genetic testing even when embryos were created earlier.