PGT, or Pre-implantation Genetic Testing, refers to the genetic screening of embryos before implantation, allowing prospective parents to select embryos with a normal genetic profile. The primary benefit of this testing is the reduced likelihood of transferring an embryo with abnormalities, thereby helping to avoid the need for selective termination later in pregnancy.

There are three basic types of pre implantation genetic testing:

• 1. Preimplantation genetic testing for aneuploidy (PGT-A):

• 2. Preimplantation genetic testing for a monogenic disease (PGT-M):

• 3. PGT for chromosome structural rearrangement (PGT-SR):

• 1. Preimplantation genetic testing for aneuploidy (PGT-A):

  PGT-A is an analysis of embryo cells to determine if there is the normal amount of chromosomes. An unequal division of either sperm or egg cells can result in an embryo having too few or too many chromosomes.
  Most people have 46 chromosomes because they inherit 23 chromosomes from each parent. If an embryo or a cell is missing a chromosome or has an extra one, it is called aneuploidy. Monosomy is a missing chromosome and trisomy is an extra chromosome.
  A child can only survive one type of monosomy, Turner syndrome, which is the absence of one of the X chromosomes. Trisomy of chromosome pairs can sometimes result in live birth, Down syndrome, also called trisomy 21 (an extra chromosome in normal pair # 21), Turner syndrome (trisomy 18) and Patau syndrome (trisomy 13). Down syndrome affects 1 in 700 babies, according to the Centers for Disease Control and Prevention.
  Aneuploidy is one of the greatest causes of failed implantation for pregnancy and miscarriage, as well as a major cause of birth defects in children.

• 2. Preimplantation genetic testing for a monogenic disease (PGT-M):

  PGT-M, or Pre-implantation Genetic Testing for Monogenic disorders, is used to screen embryos for specific gene mutations that one or both parents are known to carry. A family history of genetic conditions in either parent can increase the risk of passing on a genetic mutation to the child. These types of disorders are caused by mutations in a single gene within the DNA sequence. This can lead to inherited conditions such as cystic fibrosis and sickle cell anaemia, or increase the risk of certain diseases, such as BRCA1 and BRCA2 mutations, which are strongly linked to a higher risk of breast and ovarian cancer in women. During the PGT-M process, embryos are tested for the relevant genetic conditions before any potential transfer to the woman’s womb.

  PGT-M is commonly used to screen for conditions including:

  • Huntington’s disease
  • Sickle cell anaemia
  • Muscular dystrophy
  • Cystic fibrosis
  • BRCA1 & BRCA2 mutations
  • Fragile X syndrome
  • Tay-Sachs disease

• 3. PGT for chromosome structural rearrangement (PGT-SR):

  PGT-SR, or Pre-implantation Genetic Testing for Structural Rearrangements, is used to analyse embryos from patients known to carry a chromosomal structural rearrangement, such as an inversion or translocation. Individuals with these rearrangements have a higher risk of producing embryos with an abnormal amount of chromosomal material. Such embryos are less likely to result in a successful live birth and are often associated with recurrent miscarriage.

  PGT-SR is used to screen for structural chromosomal disorders including:

  • Robertsonian translocations
  • Reciprocal translocations
  • Non-reciprocal translocations