Preimplantation Genetic Screening (PGS) is a term formerly used for the process now known as Preimplantation Genetic Testing for Aneuploidy (PGT-A). This specialized test is performed on embryos created through In Vitro Fertilization (IVF) to check for an abnormal number of chromosomes, a condition called aneuploidy. Identifying chromosomally normal embryos helps improve the chance of a successful pregnancy and reduces the risk of miscarriage. The timeline for receiving these results is variable, but the typical waiting period is between one and three weeks.
Preparing the Embryos for Testing
The process of genetic testing begins after the eggs are retrieved and fertilized. Embryos must first be cultured for five to six days until they reach the blastocyst stage. This stage is when the embryo has developed into two distinct cell groups and is composed of several hundred cells.
Once the embryo reaches this developmental milestone, a small procedure called a trophectoderm biopsy is performed. A few cells, typically five to eight, are removed from the trophectoderm, the outer layer of cells that will eventually form the placenta. The inner cell mass, which develops into the fetus, is not disturbed during this process.
Immediately following the biopsy, the embryo is cryopreserved, or frozen, in liquid nitrogen. Freezing is necessary because the subsequent genetic analysis takes several days to complete, making a fresh embryo transfer in the same cycle impossible. The biopsied cells are then placed in a tube and prepared for shipment to the genetic testing laboratory.
The Standard Laboratory Processing Time
The countdown for the PGT-A results begins once the laboratory receives the biopsied cell samples. The standard turnaround time for the analysis ranges from seven to fourteen calendar days. This timeframe includes several distinct scientific steps that must be executed to ensure result accuracy.
The initial phase involves shipping the samples from the IVF clinic to the reference lab, which typically takes one to two days. Once received, the tiny amount of DNA must be multiplied through whole genome amplification to generate enough material for testing. This amplification and the subsequent analysis using Next-Generation Sequencing (NGS) technology can take between four and seven days.
The sequencing process generates vast amounts of data regarding the chromosome count of each embryo. Specialized geneticists and bioinformaticians then spend two to five days analyzing this data, performing quality control checks, and generating a final report. The total time is influenced by the lab’s specific workflow and the volume of samples they are processing.
Common Causes of Delays in Receiving Results
While the standard timeframe is about two weeks, several factors can extend the wait for PGT-A results. One common reason for delays is an initial failure to obtain a conclusive diagnosis, often referred to as a “no result” or “uninformative” result. This issue is caused by an insufficient amount of DNA in the biopsy sample or a technical failure during the DNA amplification step.
When an inconclusive result occurs, the clinic may offer the option to re-biopsy the frozen embryo and send a new sample for analysis, which adds another week or more to the timeline. Logistical issues can also contribute to delays, particularly if the sample must be shipped internationally or if transport is disrupted by weather or holidays. High patient volume at the laboratory can also create a backlog, pushing the results closer to the three-week mark or beyond.
Integrating PGS Results into the Treatment Schedule
Once the PGT-A results are released from the laboratory, they are sent directly to the fertility clinic. The medical team reviews the report to determine which embryos are chromosomally normal (euploid) and therefore viable for transfer. The results dictate the next clinical action, which is planning a Frozen Embryo Transfer (FET) cycle.
Because the embryos were frozen after the biopsy, a transfer cannot be attempted until the next menstrual cycle. The patient’s next cycle is typically used to prepare the uterine lining with specific hormonal medications, such as estrogen and progesterone, to make it receptive for implantation. This preparation process adds an additional two to four weeks to the overall treatment schedule. The PGT-A results provide the necessary information to select the best embryo and schedule the subsequent FET.