If you are undergoing fertility treatment and have heard of Preimplantation Genetic Screening (PGS), you may be wondering what it is and if it’s something that might be beneficial for you. If you’re doing In Vitro Fertilization (IVF) that does not include Preimplantation Genetic Screening, embryos are chosen primarily on their visual quality (morphology). This does not distinguish chromosomally normal embryos from chromosomally abnormal embryos. IVF cycles that do include Preimplantation Genetic Screening help select chromosomally normal embryos for future transfers. PGS improves success rates of transfers and helps patients achieve successful pregnancies and a healthy baby. Therefore talking to your doctor about PGS might be something you may want to consider.
How Preimplantation Genetic Screening WorksWith Preimplantation Genetic Screening, a biopsy is typically taken at blastocyst stage which is usually achieved at day five or day six of embryo development. Embryologists perform embryo biopsies by removing 4-6 cells out of the 100-200 cell blastocyst. The biopsy is then sent to a lab for Preimplantation Genetic Screening analysis. Typically, the embryos are frozen and remain at the fertility clinic while the biopsies are analyzed at the lab. Preimplantation Genetic Screening screens each embryo biopsy and quantifies the number of chromosomes in each sample. A normal embryo should contain 46 chromosomes or 23 pairs of chromosomes in total, with one set contributed by the sperm source and the other set contributed by the egg source. Embryos determined to be chromosomally normal or euploid have a much higher chance of implantation, ongoing pregnancy and resulting in a healthy baby compared to abnormal embryos. If there is any deviation from the typical 46 chromosomes, the embryo is diagnosed as abnormal or aneuploid. If the embryo is considered aneuploid, that means there are one or more missing or extra chromosomes. If an embryo has a missing or extra chromosome it is likely to result in a failed implantation, miscarriage, or a pregnancy affected with a chromosomal syndrome. Once all the embryos are analyzed, a genetic report is sent back to your reproductive endocrinologist. Your doctor will use the results in combination with the grading/morphology of the embryos to make a recommendation about which embryo to transfer. Recently, the American Society for Reproductive Medicine, The European Society of Human Reproduction and Embryology and The International Committee Monitoring Assisted Reproductive Technologies decided to start using the term Preimplantation Genetic Testing for Aneuploidies (PGT-A) instead of Preimplantation Genetic Screening (PGS). These terms are often used interchangeably.
Who Should Consider Preimplantation Genetic Screening?Preimplantation Genetic Screening increases the success rates of frozen embryo transfers. Although PGS requires an additional step in the IVF process, this screening can significantly reduce the risk for miscarriage and failed transfers. It is also important to understand that as women age, the chance of chromosome abnormality increases. If you’re over the age of 35 years old, you may want to discuss Preimplantation Genetic Screening with your fertility doctor. However, even in young women there is still a fairly high risk for chromosomal errors in embryos. PGS is recommended for women of any age who have experienced recurrent miscarriage, whether they conceived naturally and/or through fertility treatment.
Benefits of Preimplantation Genetic Screening with your IVF treatmentChromosomal abnormalities are often responsible for roughly 70 percent of miscarriages in early pregnancy. Therefore, Preimplantation Genetic Screening can increase your chance of a successful pregnancy. In addition to some of the benefits we’ve highlighted above, other benefits are:
- Increases the chance of a healthy pregnancy across all age groups
- Higher pregnancy rates per transfer
- Fewer cycles of IVF treatment needed (less time and money)
- Allows for single-embryo transfer by identifying the embryo that has the best chances of implanting and leading to a healthy child. Single Embryo Transfer (SET) can help reduce the possibility of health complications that are often associated with twin and/or triplet pregnancies. Multiple pregnancies can also possibly cause increased risk for complications during pregnancy, such as preterm birth, abnormal placental function, preeclampsia, and NICU costs.
- If you use Preimplantation Genetic Screening, it can reduce the amount of time in between IVF cycles. For example: If you go through an IVF cycle and a normal embryo is not identified, you can start your next cycle right away.