Preimplantation Genetic Testing (PGT)

Preimplantation genetic testing (or PGT) is a type of genetic test healthcare providers can perform on embryos created through in-vitro fertilization (IVF). It allows your fertility specialist to screen embryos for certain genetic or chromosomal conditions before they transfer the embryo into your uterus.

Embryos with these types of conditions have a lower chance of implantation and a higher chance of miscarriage. Results of PGT testing allows couples to select embryos that don’t contain genetic or chromosomal disorders, which then increases their chances of a healthy pregnancy. It can also prevent them from passing on a potentially life-threatening condition to their child.

PGT is a tool fertility specialists can use to help couples pursuing IVF achieve the best chance at a healthy pregnancy and healthy child. It can prevent you from passing down a genetic disease or continuing with the IVF process when it’s likely to be unsuccessful. It can also help couples select the embryo that has the sex they desire.

PGT is different from a prenatal genetic test called a carrier screen. The genetic carrier screening can detect small changes in the genes of the birth parents. If both you and your partner are carriers of the same condition, the embryo you create has a higher chance of having that single-gene condition. People who are carriers of single-gene conditions may choose to have PGT to test their embryos.

PGT is also called:

• PGT or preimplantation genetic diagnosis (PGD)
• PGS or preimplantation genetic screening (PGS)

Couples considering PGT should talk to their healthcare team about the risks and benefits of testing their embryos. A genetic counselor can also help you understand your situation and recommend the type of testing that’s right for you.

What are reasons for getting PGT?

People undergoing IVF may choose preimplantation genetic testing (PGT) to check embryos for genetic and/or chromosomal conditions. This information can help prevent transferring an embryo with a significant medical condition or one that is less likely to implant and more likely lead to miscarriage.

You may decide to have this test if:

• Either you or your partner has a history of inheritable genetic mutations, including conditions like cystic fibrosis
• You have a history of recurrent miscarriage due to chromosomal abnormalities
• You’re of advanced age and at risk of having children with a chromosomal abnormality, like Down syndrome
• You have unexplained infertility or a history of unsuccessful fertility treatment

Types of PGT

Fertility specialists can perform three different types of preimplantation genetic testing:

1. Preimplantation genetic screening for abnormal chromosome number (PGT-A).
2. Preimplantation genetic testing for monogenic (or single gene) disease (PGT-M).
3. Preimplantation genetic testing for chromosomal rearrangements (PGT-SR).

PGT-A

The “A” stands for aneuploid, which is a condition where a cell has excess or missing chromosomes. It’s one of the leading causes of failed implantation and miscarriage. This type of test checks whether the embryo has 46 chromosomes (23 from each parent). An embryo that has more or fewer than 46 chromosomes is less likely to result in a healthy pregnancy. Examples of chromosomal disorders include Down syndrome, Turner syndrome and Patau syndrome.

PGT-M

This test checks the embryo for a specific condition that one (or both) of the birth parents carries. When both parents are carriers of genetic conditions, the chance of them passing it on to their child is higher. This test checks the embryo for such conditions. Examples of single-gene diseases are sickle cell anemia, cystic fibrosis, muscular dystrophy and spinal muscular atrophy.

It also identifies human leukocyte antigen (HLA)-compatible embryos. This is helpful when a sibling of the developing embryo needs a bone marrow transplant.

PGT-SR

Chromosomal rearrangements describe chromosomes that appear structurally different. The main types of rearrangements are inversion and translocation. Both types mean that the genetic material of the embryo contains errors that could lead to serious health problems and repeat miscarriages.