What is Preimplantation Genetic Testing (PGT) A?

From the Guidelines

PGT-A, or Preimplantation Genetic Testing for Aneuploidy, is a screening method used during in vitro fertilization (IVF) to identify embryos with abnormal chromosome numbers before they are transferred to the uterus, and its use is particularly beneficial for women of advanced maternal age, those with recurrent pregnancy loss, or couples with previous failed IVF attempts, as it can improve live birth rates and reduce the risk of miscarriage and birth defects 1.

Key Points to Consider

• PGT-A involves removing a few cells from a developing embryo at the blastocyst stage, analyzing these cells for chromosomal abnormalities, and selecting embryos with normal chromosome counts for transfer.
• The procedure can detect conditions like Down syndrome (trisomy 21), Turner syndrome (monosomy X), and other chromosomal abnormalities that might lead to implantation failure, miscarriage, or birth defects.
• However, PGT-A has limitations - it cannot detect all genetic disorders, may occasionally provide false results, and adds significant cost to IVF treatment.
• The embryo biopsy process also carries a small risk of damaging the embryo, though modern techniques have minimized this risk considerably.
• A recent study noted that ongoing pregnancy rates and live birth rates are improved in those of advanced age (≥ 38) with the implementation of PGT-A, but the conclusion is not straightforward due to the lack of viable embryos to transfer in some cases 1.

Clinical Utility and Regulation

• The clinical utility of PGT-A to select euploid embryos remains controversial because of lack of proof of efficacy in increasing live births.
• The American College of Obstetricians and Gynecologists (ACOG) states that routine use of PGT-A for IVF in infertile women is not proven.
• There is a need for strict oversight on the regulation of PGT-A, as it is widely utilized by reproductive endocrinologists without clinical validation.

Recommendations for Use

• The use of PGT-A should be considered on a case-by-case basis, taking into account the individual's medical history, age, and risk factors, as well as the potential benefits and limitations of the procedure 1.
• Patients should be fully informed about the risks and benefits of PGT-A, including the potential for false results, the cost of the procedure, and the risk of damaging the embryo.
• Further research is needed to confirm the analytical and clinical validity of PGT-A before its widespread adoption in clinical practice.

From the Research

Definition of PGT-A

• PGT-A stands for Preimplantation Genetic Testing for Aneuploidy, a screening test applied to embryos created from in vitro fertilization to diminish the chance of an aneuploid conception 2, 3, 4.
• The objective of PGT-A is to select for transfer a euploid embryo, after embryo biopsy and cytogenetic analysis, to improve pregnancy success 2, 3.

How PGT-A Works

• The current technique consists of applying comprehensive chromosome screening on trophectoderm cells after blastocyst-stage embryo biopsy 3.
• PGT-A seeks to identify preimplantation embryos with a normal chromosome complement (euploid) and exclude those with abnormal chromosome numbers (aneuploid) 2.

Effectiveness of PGT-A

• Earlier versions of PGT-A were ineffective, and in some cases, detrimental, due to biopsy-induced trauma and because the technology at the time could analyze only a fraction of all chromosomes 2.
• More recent studies have shown that PGT-A can be an effective tool for embryo selection, particularly for patients with normal ovarian reserve 3, 5.
• However, the liberal use of PGT-A for other patient populations has not yet been shown to be effective, or indeed, without harm 2.

Limitations of PGT-A

• The accuracy of PGT-A results can be limited, particularly for mosaic embryos, which can lead to misdiagnosis and incorrect transfer decisions 6, 4.
• The rate of misdiagnosis for both false aneuploidy (false positive) and false euploidy (false negative) test results is unknown, and further research is needed to determine the diagnostic accuracy of PGT-A 4.