Preimplantation Genetic Testing (PGT)

Preimplantation Genetic Testing (PGT) involves several steps, starting with an in vitro fertilization (IVF) cycle to produce multiple embryos. After the eggs are fertilized with sperm in the laboratory and the embryos develop to a certain stage (typically day 3 or day 5 of growth), a small biopsy of cells is taken from each embryo. The biopsy can involve removing a single cell from a day-3 embryo (cleavage stage) or several cells from the trophectoderm of a day-5 blastocyst (blastocyst stage). The DNA from the biopsied cells of each embryo is then analyzed to determine if it carries any specific genetic or chromosomal abnormalities. There are different types of PGT:

• PGT-A (Preimplantation Genetic Testing for Aneuploidy): Screens the number of chromosomes in the embryo to identify if there is an abnormal number (gain or loss), such as trisomy 21 (Down syndrome).
• PGT-M (Preimplantation Genetic Testing for Monogenic/Single Gene Defects): Tests embryos for specific inherited disorders caused by mutations in a single gene, such as cystic fibrosis or Huntington's disease. This testing usually requires knowing the specific gene mutation present in the family.
• PGT-SR (Preimplantation Genetic Testing for Chromosomal Structural Rearrangements): Screens embryos for structural rearrangements in the chromosomes, such as translocations or inversions, which may not cause problems for the carrier parent but can lead to embryos with an unbalanced number of genes. The results of PGT testing typically take a few days to a week. During this time, the embryos are cryopreserved (frozen). Once the results are available, the embryos identified as genetically normal are selected for transfer to the mother's uterus in a subsequent frozen embryo transfer cycle. PGT can significantly increase the chances of successful pregnancy and reduce the risk of having a child with a known genetic disorder.

• Symptoms: Preimplantation Genetic Testing (PGT) does not involve any direct symptoms experienced by the intended parents. It is a diagnostic technique performed on the embryos in the laboratory. Women undergoing the IVF cycle may experience symptoms related to ovarian stimulation and egg retrieval.
• Causes (Why Preimplantation Genetic Testing - PGT is Performed):
  • Family History of Genetic Disorders: When one or both parents have a family history of a single-gene disorder (PGT-M).
  • Carrier of a Known Genetic Mutation: When one parent is a carrier of a gene mutation that can be passed on to the child (PGT-M).
  • History of Pregnancies Affected by Genetic Disorders: Having a previous child with a genetic disorder.
  • History of Recurrent Miscarriage: Which may be due to chromosomal abnormalities in the embryos (PGT-A).
  • Repeated In Vitro Fertilization (IVF) Failure: Which may be due to embryos with an abnormal number of chromosomes (PGT-A).
  • Advanced Maternal Age: Associated with an increased risk of producing embryos with an abnormal number of chromosomes (PGT-A).
  • Carrier of a Chromosomal Structural Rearrangement: When one parent carries a structural rearrangement in their chromosomes (PGT-SR).

• Diagnosis (to determine the need for PGT):
  • Genetic Evaluation and Family History: A genetic counselor assesses the couple's medical and family history to determine the risk of a genetic or chromosomal disorder.
  • Genetic Testing of Parents: May involve blood tests to identify if either parent carries gene mutations or has chromosomal abnormalities.
  • PGT Consultation: Discussing the benefits, risks, and limitations of PGT with the couple.
• Treatment Stages (The PGT Process):
  • In Vitro Fertilization (IVF) Cycle: Involves ovarian stimulation, egg retrieval, and fertilization of the eggs with sperm in the laboratory to create embryos.
  • Embryo Culture: The embryos are grown in the laboratory until they reach a suitable stage for biopsy (day 3 or day 5).
  • Embryo Biopsy: Removal of a single cell or several cells from each embryo by a trained embryologist.
  • Embryo Cryopreservation: The biopsied embryos are frozen while the cells are being analyzed.
  • DNA Analysis: The biopsied cells are sent to a specialized genetics laboratory for analysis to screen for the targeted genetic or chromosomal disorders.
  • Receiving Results: The couple is informed of the test results and which embryos are genetically normal.
  • Frozen Embryo Transfer Cycle: A healthy embryo is thawed and transferred to the mother's uterus in a medicated cycle.
  • Pregnancy Test: A pregnancy test is performed approximately two weeks after the embryo transfer.
  • Follow-up: In case of a successful pregnancy, the pregnancy is followed normally.