In U.S. IVF (in vitro fertilization) treatments, you may often hear about PGT (Preimplantation Genetic Testing) and PGS (Preimplantation Genetic Screening). While they are related, there are important distinctions in their meaning and application. This article explains the differences between PGT and PGS and provides an overview of key IVF technologies used in the U.S.
1. What Are PGT and PGS?
1. PGT (Preimplantation Genetic Testing)
PGT is an umbrella term for all genetic tests performed on embryos before implantation. It includes three main types:
- PGT-A (Aneuploidy): Screening for abnormal numbers of chromosomes (previously called PGS)
- PGT-M (Monogenic): Testing for single-gene inherited disorders
- PGT-SR (Structural Rearrangements): Detecting chromosomal structural abnormalities such as translocations or inversions
2. PGS (Preimplantation Genetic Screening)
PGS is a subset of PGT, specifically referring to routine screening for chromosomal number and structure abnormalities, now generally known as PGT-A. The primary goal is to exclude embryos with aneuploidy (abnormal chromosome count) to improve success rates and reduce miscarriage risk.
2. Summary of Differences Between PGT and PGS
| Term | What It Tests | Main Purpose | Suitable For |
|---|---|---|---|
| PGT | Chromosome number, single-gene diseases, structural abnormalities | Comprehensive genetic testing addressing various genetic issues | Older women, genetic carriers, patients with recurrent IVF failure |
| PGS (PGT-A) | Only chromosome number abnormalities (aneuploidy) | Screening for embryos with normal chromosome count | Most older patients, those with miscarriage history |
3. Advantages of PGT Technology in U.S. IVF
- Accurate diagnosis: Detects genetic abnormalities in embryos to exclude unhealthy ones
- Improved success rates: Transfers only healthy embryos, increasing implantation and live birth chances
- Reduced miscarriage rates: Avoids embryos with chromosomal abnormalities that cause miscarriage
- Prevention of genetic disease transmission: Crucial for families carrying single-gene disorders
- Reduced multiple pregnancy risk: Confident single embryo transfer promotes maternal and fetal health
4. Other Common U.S. Assisted Reproductive Technologies
- Blastocyst Culture
Culturing embryos to day 5–6 blastocyst stage to increase the proportion of high-quality embryos suitable for PGT. - Frozen Embryo Transfer (FET)
Freezing embryos for transfer at the optimal uterine environment, improving success rates. - Egg or Sperm Freezing
Preservation for future fertility, especially useful for older patients or those with special needs. - Assisted Hatching
Thinning or opening the embryo’s outer shell to facilitate implantation.
5. Conclusion
PGT is the general term for all genetic testing performed before embryo implantation, covering multiple types of screening, while PGS specifically refers to chromosome number screening (now called PGT-A). Advanced U.S. reproductive technologies combined with PGT have greatly enhanced IVF success rates and safety.