Preimplantation Genetic Testing (PGT) involves studying the DNA of embryos created in a laboratory through in vitro fertilization (IVF) before they are implanted into the uterus. It can detect hundreds of different genetic disorders, such as chromosome abnormalities and single-gene diseases. Couples who wish to avoid passing on a hereditary disease to their children can choose to only transfer healthy embryos. PGT can reduce the chance of a child with a serious chromosomal disorder by >95%.

Hereditary diseases account for 20% of infant deaths in developed countries. These are caused by genetic mutations that are present in the sperm or eggs of the parents. These mutations can cause a decrease in the chances of conceiving a healthy child, and they can also be associated with miscarriage. Currently, there are three clinical indications for using PGT with IVF: screening for aneuploidy (PGT-A), testing for monogenic disorders (PGT-M), and testing for chromosomal structural abnormalities (PGT-SR).

In the case of aneuploidy, PGT can detect chromosomal abnormalities that may be present in embryos that have been conceived through conventional IVF methods. This is especially helpful for older women who are at higher risk of having aneuploid embryos, as well as couples who have experienced chromosomal abnormalities in previous pregnancy loss or implantation failure. It can also be used for patients who are at high risk of passing on a recessive genetic disease to their offspring (such as cystic fibrosis or sickle cell anemia) or those with X-linked diseases such as fragile X syndrome and hemophilia A.

There are two types of PGT: screening for aneuploidy and testing for monogenic diseases.To perform PGT-A (testing for aneuploidy), doctors first remove a woman’s eggs. These are fertilized in the lab with a man’s sperm and then cultured into multiple embryos. A few cells from each embryo are then removed and tested for chromosomal abnormalities, such as an extra or missing chromosome. Only embryos with normal chromosomes are transferred into the uterus, and the remaining embryos can be frozen for later use. To detect aneuploidy, doctors look at the number of chromosomes in each embryo. A typical embryo has 46 chromosomes, so an embryo with an extra chromosome would be considered aneuploid and could lead to Down’s syndrome or other trisomy disorders.

PGT for monogenic diseases can identify embryos with single gene disorders such as sickle cell disease, spinal muscular atrophy type 1, and hereditary hemochromatosis. In addition, PGT can screen for chromosomal structural abnormalities such as balanced translocations.

Both forms of PGT require a very small sample of cells from each embryo. This is done through a minimally invasive procedure that involves a small puncture in the outer layer of the embryo. It is a very safe technique. It is recommended that couples considering PGT undergo a careful process of shared decision-making with their doctor, involving discussion of the benefits, risks, and limitations of the test. In the UK, for example, the Human Fertilisation and Embryology Authority (HFEA) requires each center to have a license for every test they offer.