Preimplantation Genetic Testing (PGT) is a diagnostic tool used during in vitro fertilization (IVF) to assess the genetic health of embryos before uterine transfer. PGT helps identify embryos with genetic abnormalities, which can improve pregnancy success and reduce miscarriage risk. It allows for more informed decisions in the IVF process.
What PGT Involves
PGT screens embryos for various genetic conditions. PGT-A (aneuploidy) screens for an abnormal number of chromosomes, a common cause of IVF failure and miscarriage. PGT-M (monogenic/single gene disorders) identifies embryos at risk for specific inherited diseases, such as cystic fibrosis or Huntington’s disease, when a known genetic mutation is present in the parents. PGT-SR (structural rearrangements) is used when parents have chromosomal structural changes that could be passed on to their offspring.
Clinics recommend PGT to increase the likelihood of a healthy pregnancy by selecting chromosomally normal embryos for transfer. The fundamental steps involve culturing embryos to a specific developmental stage, typically the blastocyst stage. A small sample of cells is then removed from each embryo via embryo biopsy. These biopsied cells are sent to a specialized genetic testing laboratory for analysis.
The PGT Process Timeline
The PGT timeline begins after eggs are retrieved and fertilized, and the resulting embryos are cultured in the laboratory. Embryos develop to the blastocyst stage, around day 5 or 6 after fertilization. At this point, a small number of cells from the trophectoderm, the embryo’s outer layer, are biopsied. This biopsy procedure is brief and does not harm the embryo’s development.
Following the biopsy, the embryos are cryopreserved, or flash-frozen, through a process called vitrification. They remain stored in liquid nitrogen while the biopsied cells are sent for genetic analysis. This freezing step is necessary because genetic testing takes time, making a fresh embryo transfer in the same cycle impractical.
The laboratory analysis is often the longest phase of the PGT process. Results for PGT-A typically become available within 1 to 3 weeks after the sample is received by the lab. For PGT-M, the initial test development can take 4 to 12 weeks, as a custom test may need to be created for the family’s specific genetic situation. Once results are ready, they are communicated from the genetic testing laboratory to the IVF clinic and then to the patient, allowing for embryo selection for a future transfer.
Factors Affecting PGT Timing
Several variables influence the PGT results timeline, including the specific type of PGT performed. PGT-M often requires a preliminary setup phase to develop a custom test for the family’s genetic mutation, adding several weeks. This setup is not typically needed for PGT-A.
Laboratory workload and efficiency also play a role; high-volume labs may take longer, and clinic coordination impacts result delivery speed.
Shipping logistics for transporting embryo biopsy samples can introduce minor delays. Holidays and weekends can further affect lab processing schedules, potentially extending the waiting period. A repeat biopsy due to an inconclusive initial result can also add unexpected time.
How PGT Affects Your IVF Cycle
The PGT timeline directly impacts the IVF journey, particularly regarding embryo transfer. Since embryos are biopsied and frozen while awaiting genetic results, a fresh embryo transfer in the same cycle is generally not possible. Instead, PGT necessitates a frozen embryo transfer (FET) cycle, where a previously frozen embryo is thawed and transferred in a subsequent menstrual cycle.
This waiting period between embryo creation and transfer typically adds a delay of at least one menstrual cycle. After receiving the PGT results, the clinic works with the patient to plan the FET, which involves preparing the uterine lining, usually with hormone medications. PGT results allow for informed decision-making, as only genetically screened embryos deemed suitable are selected for transfer.
While PGT adds time to the overall IVF process, often extending it by several weeks, it is frequently considered a valuable step. This extended timeline is a trade-off for the benefits of selecting embryos with a higher chance of successful implantation and a healthy pregnancy.