In vitro fertilization (IVF) is a widely used fertility treatment that assists individuals and couples in conceiving. This process involves fertilizing an egg with sperm outside the body in a laboratory setting. Over time, IVF techniques have advanced significantly, incorporating sophisticated methods designed to enhance the likelihood of a successful pregnancy.
Understanding PGT
Preimplantation Genetic Testing, or PGT, is a specialized procedure performed on embryos created through IVF before they are transferred to the uterus. This testing evaluates embryos for chromosomal abnormalities or specific genetic conditions. The primary goal of PGT is to identify embryos with the highest potential for a healthy outcome, thereby increasing the chances of a successful pregnancy and the birth of a healthy child.
Specific Applications of PGT
PGT is categorized into three main types, each designed to detect different genetic concerns in embryos.
PGT-A
PGT-A, or Preimplantation Genetic Testing for Aneuploidy, screens embryos for an abnormal number of chromosomes. Aneuploidy, such as having an extra chromosome (trisomy) or a missing chromosome (monosomy), is a common reason for failed implantation, miscarriage, or genetic disorders like Down syndrome. PGT-A is often considered for individuals of advanced maternal age, as the risk of aneuploidy increases with age, and for those with a history of recurrent pregnancy loss or multiple failed IVF cycles.
PGT-M
PGT-M, or Preimplantation Genetic Testing for Monogenic Disorders, is utilized when there is a known risk of passing on a specific inherited single-gene disorder. This includes conditions such as cystic fibrosis, sickle cell anemia, or Huntington’s disease, where parents are known carriers or are affected themselves. PGT-M involves creating a unique test tailored to the family’s specific genetic mutation to identify unaffected embryos.
PGT-SR
PGT-SR, or Preimplantation Genetic Testing for Structural Rearrangements, is performed for individuals who carry chromosomal structural rearrangements. These rearrangements, such as translocations or inversions, can lead to embryos with an incorrect amount of chromosomal material, potentially causing recurrent miscarriages or birth defects. PGT-SR identifies embryos that have a balanced set of chromosomes, increasing the likelihood of a successful pregnancy and reducing the risk associated with these rearrangements.
The PGT Process
The PGT process integrates seamlessly within an IVF cycle, beginning with the development of embryos in the laboratory. After eggs are fertilized with sperm, the resulting embryos are cultured for several days, typically reaching the blastocyst stage by day five or six.
At this stage, the embryo has differentiated into two main cell types: the inner cell mass, which will form the fetus, and the trophectoderm, which will develop into the placenta.
Once the embryos reach the blastocyst stage, a delicate procedure called an embryo biopsy is performed. A few cells are carefully removed from the trophectoderm layer of each embryo using a specialized laser. This approach minimizes potential impact on the developing fetus, as the cells are taken from the part that forms the placenta.
The biopsied embryos are then typically frozen while awaiting genetic analysis results. The extracted cells are sent to a specialized laboratory for comprehensive genetic analysis. Depending on the type of PGT being performed, the laboratory will assess the cells for chromosomal numbers, specific gene mutations, or structural rearrangements. Once the results are available, they are shared with the fertility team and prospective parents. Based on these PGT results, embryos identified as genetically normal or unaffected by the specific condition being tested for are selected for transfer into the uterus.
Factors Influencing PGT Decisions
Several factors lead individuals and couples to consider PGT. These include advanced maternal age, a history of recurrent pregnancy loss, multiple unsuccessful IVF cycles, or when one or both partners are known carriers of a specific genetic disease or chromosomal structural rearrangement.
While PGT offers valuable insights, important considerations exist. PGT results may be inconclusive for some embryos, or that no genetically normal embryos are identified for transfer. Although rare, there is a minimal potential for harm to the embryo during the biopsy procedure.
The financial investment associated with PGT can also be substantial, as it adds to the overall cost of IVF treatment, and insurance coverage varies. Comprehensive genetic counseling provides detailed information about PGT implications, helping individuals make informed choices.