Preimplantation genetic diagnosis of embryos (PGD)

Preimplantation Genetic Diagnosis (PGD) is a genetic testing method used as part of in vitro fertilization (IVF). The purpose of PGD is to identify potential genetic or chromosomal abnormalities in embryos before they are transferred into the uterine cavity. This approach helps increase the likelihood of successful conception and the birth of a healthy child, while reducing the risk of transmitting hereditary diseases.

When is PGD used?

In Belarus, preimplantation genetic diagnosis is most commonly performed in the following situations:

• Risk of hereditary diseases: if there is a family history of genetic disorders (such as cystic fibrosis, hemophilia, or muscular dystrophy), PGD can help prevent transmission of these conditions to offspring.
• Parental age: PGD is recommended for women over 35 years of age or men over 40, as the risk of chromosomal abnormalities increases with age.
• Recurrent miscarriages or failed IVF cycles: PGD helps identify chromosomal abnormalities that may be responsible for repeated pregnancy loss or unsuccessful IVF attempts.
• Male factor infertility: in cases of poor sperm quality or a high level of sperm DNA fragmentation, PGD can assist in selecting genetically healthy embryos.
• Genetic screening for monogenic disorders: PGD enables detection of embryos that carry specific gene mutations associated with severe inherited diseases.

How is preimplantation genetic diagnosis performed?

PGD is an integral part of the IVF process and is carried out prior to embryo transfer into the uterine cavity. The procedure includes several stages:

• IVF and embryo development: first, in vitro fertilization (IVF) is performed, during which the woman’s eggs are fertilized with the man’s sperm in a laboratory setting. The embryos are cultured for 3–5 days until they reach the blastocyst stage.
• Embryo biopsy: on day 5 of development, several cells are taken from the outer layer of the embryo (the trophectoderm), which later forms the placenta. This procedure does not affect embryo development or implantation potential.
• Genetic analysis: the sampled cells are sent to a genetic laboratory to assess chromosomal abnormalities (such as trisomies associated with Down syndrome) and gene mutations linked to monogenic disorders. 
• Embryo selection: following genetic analysis, embryologists select genetically healthy embryos without detected abnormalities.
• Embryo transfer: one or more healthy embryos are transferred into the uterine cavity for further development and potential pregnancy.

Benefits of PGD

• Reduced risk of inherited diseases: PGD helps to identify pathogenic genetic mutations which allows to prevent transmission of hereditary diseases to a future child.
• Higher chances of successful pregnancy: Using embryos without genetic abnormalities increases the likelihood of successfull implantation and reduces the risk of miscarriage.
• Lower risk of chromosomal abnormalities: PGD helps to identify such abnormalities as trisomies (e.g., Down syndrome), which is particularly relevant for advanced maternal age.
• Optimization of IVF procedure: PGD allows to reduce the number of IVF cycles, as only healthy emryos are used, which increases the chances of successful pregnancy.

Types of PGD

Different types of PGD are used depending on diagnostic goals:

• PGT-A (preimplantation genetic testing for aneuploidies) — screening for chromosomal abnormalities such as trisomies or monosomies.
• PGT-M (preimplantation genetic testing for monogenic diseases) — detection of single-gene disorders such as cystic fibrosis, Marfan syndrome, hemophilia, and others.
• PGT-SR (preimplantation genetic testing for structural rearrangements) — identification of chromosomal structural changes, including inversions and translocations.

Although PGD is considered a relatively safe procedure, certain limitations exist:

• Diagnostic errors: despite high accuracy, rare cases of misclassification of embryos may occur.
• Absence of healthy embryos: in rare situations, all embryos may carry genetic abnormalities, making transfer impossible.

Preimplantation genetic diagnosis is a key tool in modern reproductive medicine, allowing not only an increase in the chances of successful conception but also a reduction in the risk of genetic and chromosomal abnormalities in future children.

In Belarus, PGD helps couples facing infertility, hereditary conditions, or age-related reproductive risks achieve their goal of becoming parents of a healthy child.