Preimplantation Genetic Testing for Aneuploidy (PGTA)

Introduction 

Preimplantation Genetic Testing for Aneuploidy (PGTA) is a procedure that is performed on embryos created through In Vitro Fertilization (IVF). This testing aims to identify chromosomal abnormalities (aneuploidies) in embryos before they are implanted in the uterus. PGTA can be particularly beneficial for couples experiencing recurrent implantation failure or those seeking to increase their chances of having a healthy pregnancy.

What is Aneuploidy?

 Aneuploidy refers to an abnormal number of chromosomes in a cell. Normal human cells have 46 chromosomes (23 pairs). Aneuploidies can lead to miscarriage, implantation failure, or genetic disorders in the child. Common types of aneuploidy include trisomy (three copies of a chromosome) and monosomy (one copy of a chromosome).

The Role of PGTA in IVF and Recurrent Implantation Failure 

Recurrent implantation failure is defined as the inability to achieve a clinical pregnancy after transferring multiple embryos. PGTA can help select embryos that are chromosomally normal (euploid), potentially increasing the chances of successful implantation and a healthy pregnancy.

Mosaicism in PGTA 

Mosaicism refers to the presence of more than one genetically distinct cell line within an embryo. Some cells may be euploid while others are aneuploid. The presence of mosaicism can complicate PGTA results and may impact embryo viability. Recent studies indicate that some mosaic embryos may still lead to successful pregnancies, though this can vary significantly based on the degree of mosaicism.

Recent Meta-Analysis Data 

A recent meta-analysis involving numerous studies has evaluated the benefits of PGTA in improving IVF outcomes. Key findings include:

1. Implantation Rates: PGTA has been shown to improve implantation rates in certain populations, particularly in women of advanced maternal age or those with a history of recurrent miscarriage (Munné et al., 2021).
2. Live Birth Rates: The data suggest that PGTA may increase live birth rates, particularly in euploid embryos, compared to non-tested embryos (Scott et al., 2022). However, results can vary, and the clinical benefit may not be significant in all patient populations.
   
3. Mosaicism Considerations: The presence of mosaic embryos can complicate decision-making. Some studies show that transferring low-level mosaic embryos can still lead to successful outcomes (Deng et al., 2023).
   

Pros and Cons of PGTA

Advantages:

• Increased likelihood of selecting chromosomally normal embryos.
• May improve implantation and live birth rates in specific patient populations.
• Helps reduce the risk of miscarriage associated with aneuploid embryos.
  

Disadvantages:

• The complexity of mosaicism 
• Potentially can hamper embryo viability if not done in a skilled manner.
• PGTA is be costly and may not be covered by insurance.
• Not all clinics offer PGTA. In Singapore, PGT-A is only allowed as part of a research project, in the restructured hospitals  and only if couples meet strict criteria.
  

Conclusion 

PGTA can be a valuable tool for couples facing recurrent implantation failure or those interested in maximizing their chances of a successful IVF outcome. However, it is essential to discuss the potential benefits and limitations with your fertility specialist, including considerations related to mosaicism.

References

1. Munné, S., et al. (2021). "The impact of aneuploidy on implantation rates: a review." Journal of Assisted Reproduction and Genetics, 38(3), 501-511.
2. Scott, R. T., et al. (2022). "Preimplantation genetic testing for aneuploidy: a clinical perspective." Fertility and Sterility, 117(6), 1200-1208.
3. Deng, Y., et al. (2023). "Clinical outcomes of transferring mosaic embryos: a systematic review and meta-analysis." Human Reproduction Update, 29(1), 100-116.
   

For more information or personalized advice, please consult your fertility specialist.