Preimplantation Genetic Testing for Aneuploidy (PGT-A) is a genetic test used during in vitro fertilization (IVF) to evaluate embryos before transfer. This process helps identify chromosomal abnormalities, aiming to improve IVF success rates and provide information for family-building decisions.
Understanding PGT-A
PGT-A screens for chromosomal abnormalities, specifically aneuploidy, which refers to an incorrect number of chromosomes in a cell. Human cells typically contain 46 chromosomes, arranged in 23 pairs.
During PGT-A, a small number of cells are biopsied from the trophectoderm, the outer layer of a blastocyst-stage embryo (typically on day 5 or 6 of development). This biopsy is then analyzed to count the chromosomes. Aneuploidy, such as having an extra chromosome (trisomy) or a missing chromosome (monosomy), can occur due to errors during egg or sperm formation or early embryonic cell division. Such chromosomal imbalances are a common reason for failed embryo implantation, miscarriage, or the development of genetic conditions like Down syndrome.
Reasons for Choosing PGT-A
By identifying and selecting embryos with the correct number of chromosomes (euploid embryos), PGT-A aims to increase implantation rates and reduce the risk of early pregnancy loss. Chromosomal abnormalities are a leading cause of miscarriage, particularly in the first trimester.
Using PGT-A can potentially shorten the overall time to achieving a successful pregnancy, as it helps avoid transferring embryos unlikely to result in a live birth. This targeted approach can reduce the number of IVF cycles and embryo transfers needed, thereby saving emotional and financial resources associated with repeated attempts. For some, PGT-A also offers reassurance by reducing the risk of a pregnancy affected by a severe chromosomal condition.
Key Considerations for Decision-Making
One significant factor is the financial investment, as PGT-A adds to the already substantial cost of IVF, typically ranging from $4,000 to $10,000 in the United States, and often not covered by insurance. While PGT-A might reduce the need for multiple transfers, potentially offsetting some costs, it represents an upfront expense.
The emotional and psychological impact of PGT-A can also be considerable. Waiting for results can be stressful, and receiving abnormal results for many or all embryos can lead to disappointment or guilt, potentially reducing the number of embryos available for transfer. Patients might feel sadness over discarding embryos identified as aneuploid, even if they are unlikely to develop into a healthy pregnancy.
PGT-A is a screening test and not 100% accurate, with reported accuracy around 98% for detecting large chromosomal imbalances. The biopsy procedure itself carries a minimal risk of damage to the embryo, though it is generally considered safe. Additionally, results can sometimes indicate mosaicism, where an embryo contains a mix of both chromosomally normal and abnormal cells.
Mosaic embryos present a complex situation, as their developmental potential varies, and some can lead to healthy live births, although typically with lower success rates than euploid embryos. The interpretation of mosaic results can vary between laboratories, and there are ongoing discussions about the best approach to managing these embryos. Discarding mosaic embryos might reduce the number of transferable embryos, potentially impacting overall IVF success, especially for individuals with fewer embryos. PGT-A is frequently recommended in specific scenarios, such as advanced maternal age (over 35), a history of recurrent pregnancy loss, multiple failed IVF cycles, or known chromosomal rearrangements in parents.
Interpreting PGT-A Outcomes
After PGT-A testing, embryos are typically classified into three main categories: euploid, aneuploid, or mosaic. Euploid embryos have the correct number of chromosomes (46) and are generally considered the most suitable for transfer, offering the highest chance of successful implantation and live birth. Aneuploid embryos, which have an abnormal number of chromosomes, are typically not recommended for transfer due to their low likelihood of resulting in a healthy pregnancy and increased risk of miscarriage or genetic conditions.
The proportion and type of abnormal cells in mosaic embryos can influence their potential. While they may have a lower chance of success compared to euploid embryos, healthy live births have been reported after their transfer. Decisions regarding mosaic embryo transfers are often made after thorough discussion with a fertility specialist and genetic counselor, who can provide personalized guidance based on the specific mosaicism identified and the individual’s circumstances. Genetic counseling is important regardless of the PGT-A outcome to ensure a complete understanding of the results and subsequent options.