What Is Preimplantation Genetic Testing (PGT)?

Preimplantation Genetic Testing (PGT) is a laboratory procedure used to analyze embryos for specific genetic conditions before implantation during an in vitro fertilization (IVF) cycle. It helps identify embryos that are free from chromosomal abnormalities or inherited genetic disorders, improving the chances of a healthy pregnancy (Wikipedia).

PGT is commonly used by individuals or couples with known genetic risks, advanced maternal age, repeated IVF failure, or recurrent pregnancy loss. By selecting genetically normal embryos, PGT aims to reduce the likelihood of miscarriage or genetic disease transmission (Mayo Clinic).

Types of Preimplantation Genetic Testing

There are three main types of PGT, each with a different clinical purpose:

1. PGT-A (for Aneuploidy)

PGT-A screens embryos for chromosomal abnormalities, such as extra or missing chromosomes. Aneuploid embryos often result in failed implantation, miscarriage, or conditions like Down syndrome. This test is typically recommended for women over 35 or couples with previous failed IVF cycles (ASRM).

2. PGT-M (for Monogenic/Single Gene Disorders)

PGT-M is used when one or both genetic parents are carriers of a single-gene disorder such as cystic fibrosis, thalassemia, or Huntington’s disease. It helps prevent the transmission of these conditions to offspring (NIH).

3. PGT-SR (for Structural Rearrangements)

PGT-SR is intended for individuals with balanced chromosomal translocations or structural rearrangements, which can lead to embryos with unbalanced genetic material. This test minimizes the risk of miscarriage or genetic abnormalities caused by structural defects (UCSF Health).

How PGT Works

PGT is performed on embryos created via IVF. After fertilization, a small number of cells are biopsied from each embryo (usually on Day 5 or 6) without harming its developmental potential. These cells are then genetically analyzed in a lab. Only embryos that are chromosomally normal or free of specific genetic conditions are selected for transfer.

This testing is optional but may be recommended based on medical history or fertility clinic protocols. Results are typically available within a few days, allowing for a fresh or frozen embryo transfer.

Who Should Consider PGT?

Preimplantation Genetic Testing may be recommended for:

• Individuals or couples with a known genetic condition

• Women aged 35 and above undergoing IVF

• Couples with recurrent miscarriages

• Previous IVF failures or poor embryo quality

• Male factor infertility with high rates of sperm DNA fragmentation

Benefits and Limitations of PGT

Benefits of PGT:

• Reduces the risk of inherited genetic disease

• Increases chances of a successful pregnancy

• Lowers risk of miscarriage due to chromosomal errors

• Allows for single embryo transfer with higher confidence

Limitations of PGT:

• Requires IVF, which may not be suitable or accessible for everyone

• May not detect all types of genetic issues

• Ethical and emotional considerations around embryo selection

• Additional costs and waiting periods for analysis

PGT does not guarantee a successful pregnancy or eliminate all risks but is a valuable tool in personalized fertility care when used appropriately (CDC).