Preimplantation Genetic Diagnosis

Preimplantation Genetic Diagnosis (PGD) is a great source of hope for couples at risk of carrying hereditary diseases. This modern medical procedure allows for the detailed examination of embryos created within the framework of IVF treatment for genetic diseases before they are placed in the mother’s womb. The primary goal of PGD is to minimize the risk of passing on known serious genetic disorders in the family to the child. This approach significantly increases the chances for couples to have a genetically healthy baby.

PGD is an advanced method applied within the scope of assisted reproductive technology. In this process, a very small cell sample is taken from the embryos and subjected to special laboratory tests. Thanks to this comprehensive embryo screening for specific genetic diseases such as cystic fibrosis, sickle cell anemia, or thalassemia, only embryos identified as genetically healthy are selected and transferred to the mother-to-be. This careful selection process prevents the transmission of the disease to future generations while also increasing the pregnancy success rate and the likelihood of a healthy birth. Thus, families can look to the future with more security and hope.

What is Preimplantation Genetic Diagnosis (PGD)?

Preimplantation Genetic Diagnosis (PGD) is a sophisticated embryo screening technique used in conjunction with IVF (in vitro fertilization) treatment. This procedure allows for the genetic assessment of embryos before they are transferred into the mother’s uterus.

Essentially, PGD acts as a comprehensive “genetic health check” for embryos, identifying those that are free from specific inherited conditions or chromosomal abnormalities. By carefully analyzing a small sample of cells from each embryo, medical professionals can select the healthiest ones, significantly increasing the chances of a successful pregnancy and the birth of a healthy baby. This detailed examination during the IVF (in vitro fertilization) process empowers prospective parents to make informed decisions about their reproductive journey.

What are the features of Preimplantation Genetic Diagnosis (PGD)?

The most significant feature of Preimplantation Genetic Diagnosis (PGD) is its ability to detect specific genetic diseases before pregnancy begins. This allows for the selection of healthy embryos prior to transfer into the uterus. PGD specifically targets known single-gene disorders, such as cystic fibrosis or Huntington’s disease, through detailed genetic testing that looks for a particular inherited mutation.

This contrasts with Preimplantation Genetic Testing for Aneuploidy (PGT-A), formerly known as PGS, which screens embryos for abnormalities in chromosome number and structure. PGT-A identifies abnormalities like an extra or missing chromosome that can lead to implantation failure, miscarriage, or conditions such as Down syndrome. While PGD prevents a specific inherited disease, PGT-A assesses the overall chromosomal health of an embryo to improve IVF success rates.

In which diseases can it be used?

Preimplantation Genetic Diagnosis (PGD) identifies a wide range of hereditary diseases and genetic conditions at the embryo stage to prevent the transmission of serious genetic disorders present in the family to future generations. The main diseases and conditions for which PGD can be used include:

• Single-Gene Diseases: It is commonly used to detect known family diseases caused by a single gene mutation. Examples include:
  • Cystic fibrosis: A serious hereditary disease affecting the lungs and digestive system.
  • Sickle cell anemia: A blood disorder that deforms red blood cells and leads to serious health problems.
  • PGD can also screen for many other single-gene genetic disorders such as Thalassemia, Huntington’s disease, and Spinal Muscular Atrophy (SMA).
• Chromosomal Abnormalities: It can be applied to detect numerical or structural chromosomal abnormalities in embryos. These abnormalities can lead to pregnancy loss or conditions like Down syndrome (Trisomy 21).
  • Cancer Predispositions: PGD is also used to detect gene mutations that increase susceptibility to certain types of cancer. For example, BRCA1 and BRCA2 gene mutations, which increase the risk of breast and ovarian cancer, can be screened in embryos.
  • HLA Tissue Typing (Savior Sibling): If there is a child in the family who requires a stem cell transplant, PGD can be used to select an HLA-compatible embryo. This method allows for the birth of a baby known as a “savior sibling” who can be a donor for the sick sibling.

These comprehensive screening methods allow parents to significantly increase the likelihood of a healthy pregnancy and birth by selecting genetically healthy embryos.

Which method is used for Preimplantation Genetic Diagnosis (PGD)?

During Preimplantation Genetic Diagnosis (PGD), several advanced genetic testing methods are applied to the embryo biopsy sample to analyze its genetic structure for hereditary diseases or chromosomal abnormalities. One of the primary techniques is Polymerase Chain Reaction (PCR), which can analyze even a tiny DNA sample by amplifying specific gene regions (amplifying DNA) to detect mutations causing single-gene disorders.

Another key method is Fluorescence In Situ Hybridization (FISH), which is used to identify numerical or structural chromosomal anomalies (counting chromosomes), such as those that can lead to conditions like Down syndrome. More recently, Next-Generation Sequencing (NGS) has become prominent, offering a far more comprehensive genetic testing capability.

How is it applied?

The Preimplantation Genetic Diagnosis (PGD) process is carried out in conjunction with IVF (in vitro fertilization) treatment and is a careful procedure involving specific steps:

1. Ovarian Stimulation and Egg Retrieval: The mother-to-be’s ovaries are stimulated with medication to develop multiple eggs. The mature eggs are collected under ultrasound guidance.
2. Fertilization and Embryo Development in the Laboratory: The collected eggs are fertilized with sperm in a laboratory environment. The resulting embryos are grown in special incubators while their development is monitored.
3. Embryo Biopsy to Obtain Cells: When the embryo reaches a specific stage of development, usually on day 3 or 5, a small cell sample (biopsy) is taken from the embryo using microscopic techniques.
4. Genetic Analysis of the Obtained Cells: The cells obtained through biopsy are analyzed in a genetic laboratory using advanced techniques like PCR or NGS. This analysis detects hereditary diseases or chromosomal abnormalities.
5. Transfer of the Healthy Embryo to the Mother’s Uterus: The embryo confirmed to be healthy as a result of the genetic analysis is selected and transferred to the mother-to-be’s uterus. This approach minimizes the risk of hereditary diseases.

How long does the application/procedure take?

The Preimplantation Genetic Diagnosis (PGD) procedure is not a single-day event but is integrated within an entire IVF cycle. The complete process, from initial consultations and the IVF cycle to genetic analysis and embryo transfer, can last from several weeks to a few months. The timeline may be extended, particularly if developing a custom genetic test for a family’s specific condition is necessary, as this preparation can take several weeks before the IVF treatment even begins.

Is the Preimplantation Genetic Diagnosis (PGD) procedure painful?

The Preimplantation Genetic Diagnosis (PGD) procedure itself is not painful for the patient, as it involves taking a cell sample from embryos in a laboratory setting. This microscopic analysis is not performed on the patient’s body. However, since PGD is applied in conjunction with IVF treatment, medical interventions such as egg retrieval are necessary. The egg retrieval process is generally performed under light anesthesia, so the patient does not feel pain. While minimal discomfort or mild cramps may be experienced after the procedure, this typically resolves quickly.

Which patients is it applied to?

Preimplantation Genetic Diagnosis (PGD) is an advanced reproductive technology recommended for specific patient groups to increase the likelihood of a healthy pregnancy. The procedure is primarily applied to couples and individuals facing particular genetic risks or reproductive challenges. Key candidates for PGD include:

• Couples with a known family history of a genetic disease: PGD is used to screen embryos for single-gene disorders such as cystic fibrosis, sickle cell anemia, or Huntington’s disease, preventing their transmission.
• Individuals or couples who are carriers of a genetic mutation: Even if asymptomatic, parents who carry a gene for a specific condition can use PGD to select unaffected embryos for transfer.
• Women of advanced maternal age: Typically over 35, these women face a higher risk of chromosomal abnormalities in their embryos. PGD helps identify chromosomally normal embryos, reducing the risk of conditions like Down syndrome.
• Patients with a history of reproductive challenges: PGD is a viable option for those who have experienced recurrent pregnancy loss or multiple failed IVF cycles, as these issues are often linked to underlying genetic problems in the embryos.

Who is not suitable for Preimplantation Genetic Diagnosis (PGD) application?

Preimplantation Genetic Diagnosis (PGD) is not a suitable method for every patient. Since PGD is a process integrated with IVF (in vitro fertilization) treatment, patients who are not medically eligible for IVF are also not candidates for PGD. Additionally, in some cases, even if a specific genetic risk factor is present, the application of PGD may not be possible due to reasons such as challenges in developing the specific genetic test or poor embryo quality.

Furthermore, PGD may not always be considered necessary for couples who do not have a known genetic risk factor and are requesting the procedure for routine screening purposes. Therefore, the applicability of PGD must be evaluated by a specialist physician based on the patient’s medical history and individual circumstances.

What are the advantages?

Preimplantation Genetic Diagnosis (PGD) offers several significant advantages for couples carrying the risk of a hereditary disease. This advanced medical method increases the likelihood of a healthy pregnancy and birth, providing considerable peace of mind for families.

The main advantages are:

• Reduces the Risk of Hereditary Disease: It significantly lowers the risk of passing on known serious genetic disorders to the child. Through embryo screening, only genetically healthy embryos are selected for transfer.
• Increases Pregnancy Success Rates: The selection of healthy embryos improves implantation success and, consequently, pregnancy rates. This is especially important for women of advanced maternal age or with a history of recurrent miscarriages.
• Avoids Difficult Decisions: Since the diagnosis is made before pregnancy, it protects couples from traumatic decisions, such as terminating a pregnancy, which could arise if a genetic disease is detected later.
• Provides Psychological Support: It offers prospective parents the chance to experience a more peaceful pregnancy, free from the anxiety of having a child with a specific genetic condition.

Are there any side effects of using Preimplantation Genetic Diagnosis (PGD)?

The risks associated with Preimplantation Genetic Diagnosis (PGD) are primarily linked to the IVF treatment it is integrated with, rather than the PGD procedure itself. The side effects experienced directly by the patient originate from the IVF process.

The risks specific to PGD are quite low. For instance, while the procedure of taking cells from the embryo (biopsy) carries a possibility of harming the embryo, this risk is very minimal. Furthermore, PGD tests do not guarantee 100% accuracy. Conditions such as embryonic mosaicism can affect the test’s precision and, on rare occasions, lead to a misdiagnosis. This situation might result in some chromosomal abnormalities being overlooked or incorrectly identified.

What should be considered after the application?

The process following embryo transfer after PGD is no different from a standard IVF transfer. During this period, it is crucial for the patient to meticulously follow the doctor’s instructions, rest, and wait until the designated time for the pregnancy test. Avoiding strenuous physical activities and stress after the transfer increases the chances of the embryo implanting in the uterus. Being patient and regularly attending scheduled check-ups are of great importance for the successful outcome of the process.