Genetic testing on frozen embryos, known as Preimplantation Genetic Testing (PGT), is possible. PGT is a procedure used with in vitro fertilization (IVF) to screen embryos for genetic conditions before transfer. This technology offers insights into an embryo’s genetic makeup, enhancing the chances of a successful pregnancy and reducing the risk of genetic disorders. The frozen state introduces specific considerations and steps.
Understanding Embryo Genetic Testing
PGT analyzes the genetic material of IVF-created embryos to identify chromosomal abnormalities or specific genetic disorders. It helps select embryos more likely to implant successfully and result in a healthy pregnancy.
There are three main categories of PGT, each screening for different genetic issues. PGT-A, or Preimplantation Genetic Testing for Aneuploidy, detects an abnormal number of chromosomes, a common cause of implantation failure or miscarriage. PGT-M, or Preimplantation Genetic Testing for Monogenic disorders, identifies specific genetic mutations that cause single-gene defects, like cystic fibrosis or Huntington’s disease. PGT-SR, or Preimplantation Genetic Testing for Structural Rearrangements, screens for structural changes within chromosomes that could affect embryo development.
The Process of Testing Frozen Embryos
Performing genetic testing on frozen embryos involves a specific sequence of laboratory procedures. First, frozen embryos are carefully thawed in a controlled environment to ensure their viability.
Following thawing, a small number of trophectoderm cells are biopsied from the embryo. This biopsy takes cells from the part of the embryo that will develop into the placenta. After the biopsy, the embryo is re-frozen, usually through vitrification, while the biopsied cells are sent for genetic analysis. This allows time for results before any potential embryo transfer. The embryo is only thawed again for transfer once genetic results are known and it is deemed suitable.
Reasons for Considering Testing Frozen Embryos
Individuals and couples consider genetic testing on frozen embryos for several reasons, often due to factors increasing the risk of genetic abnormalities or impacting IVF success. Advanced parental age is a common indication, as the risk of chromosomal abnormalities increases with the egg provider’s age. For example, the percentage of genetically abnormal embryos can significantly increase for women over 40.
Recurrent pregnancy loss is another scenario where PGT is often considered, as genetic issues can contribute to repeated miscarriages. Unexplained implantation failures in prior IVF cycles can also lead individuals to pursue PGT, seeking healthier embryos for transfer. If one or both parents are known carriers of a specific genetic disorder, such as cystic fibrosis or Huntington’s disease, PGT-M can select embryos free of the condition. PGT-SR is relevant if a parent has a known balanced chromosomal rearrangement, helping identify embryos with unbalanced forms that could lead to developmental issues.
Important Considerations and Limitations
While genetic testing on frozen embryos offers benefits, limitations exist. The process of thawing and re-freezing embryos carries a small risk to viability, though vitrification techniques have high success rates. Around 5% of embryos may not survive the freeze-thaw or biopsy.
PGT is highly accurate but not 100% perfect, with a small chance of false positives or negatives. This can lead to discarding a healthy embryo or transferring an abnormal one. PGT cannot screen for all genetic conditions or birth defects and does not replace prenatal testing during pregnancy.
Ethical and emotional aspects also play a role, as individuals may face complex decisions about which embryos to transfer based on genetic results. PGT adds to the overall cost of the IVF process. Consultation with fertility specialists and genetic counselors is recommended to understand individual risks and benefits.