Who is suitable for pre-implantation genetic diagnosis/screening (PGD/NGS)?

• Couples facing difficulties in conceiving.
• Women who are over 35 years old and desire to have children.
• Couples who have a history of recurrent pregnancy loss (more than 2 times) without a known cause.
• Couples who have undergone IVF treatment more than 2 times without successful outcomes.
• Couples who have previously experienced pregnancies with chromosomal abnormalities.

Steps for pre-implantation genetic diagnosis

The process is similar to the process of IVF in every aspect, starting from the initial stimulation of the egg until the preparation stage of the general embryo. Generally, there are three stages of appropriate embryo growth for the purpose of extracting cells for genetic diagnosis, which are as follows:

1. The pre-implantation stage of the egg or the embryo in the pre-division stage, where the polar body of the egg cell or the embryo in the pre-division stage is separated for genetic testing.

2. The embryo in the cleavage stage, which occurs three days after fertilization.

3. The embryo in the blastocyst stage, where doctors usually examine the embryo at this stage due to the sufficient number of cells that can be extracted for testing without significantly impacting the minimal growth of the embryo. Genetic differences between each cell or what is known as mosaicism are found to be less than the examination of embryos in the cleavage stage. After obtaining the embryo and nurturing it until it reaches a stage where the cell division of the embryo has a sufficient number of cells, typically around day 3-5. After fertilization, the cells of each embryo are extracted for genetic testing to determine the status of the embryo, whether it is normal or not. Then, embryos without genetic disorders are selected to be transferred back into the uterus to establish pregnancy. Currently, it is widely accepted that babies born after undergoing this genetic testing process do not differ from naturally conceived babies. Therefore, the aforementioned testing is an examination of the genetic makeup of representative cells of the entire embryo.  This testing is delicate and challenging compared to genetic testing from blood or other tissues because the amount of genetic material in a single cell is very minimal. The testing process relies on delicate precision, time, and the expertise of experienced physicians and scientists to ensure accuracy, precision, and minimal disturbance to the embryos.

Blastocentesis

Blastocentesis is the process of aspirating blastocyst fluids (BFs) in order to analyze the chromosomal composition of the respective embryos. It has been discovered that blastocyst fluids contain a significant amount of cell-free DNA, which can be used for chromosomal analysis. This method involves aspirating the fluids instead of extracting blastomeres or trophectoderm cells for analysis. One of the advantages of this method, similar to the previous method, is that it reduces disturbance to the embryo’s growth by minimizing the number of cells aspirated for testing. This allows the embryo to develop into a higher-quality fetus. In addition, blastocentesis, which is performed at the blastocyst stage when the embryo is at its most advanced stage of development before implantation, reduces the likelihood of genetic differences between individual cells compared to the traditional testing method, which may examine embryos as early as day 3. Testing at a younger age increases the chances of mosaicism. When comparing the results of chromosomal analysis from blastocyst fluid aspiration to the conventional cell extraction method, it has been found that the results are highly consistent and satisfactory.

Techniques for embryo genetic testing

There are several methods available for embryo genetic testing, each with varying degrees of accuracy. The Genesis Fertility Center has carefully selected the most advanced and accurate techniques for use in treatment, ensuring that couples receiving care at the clinic can have confidence in receiving the best available techniques.

Comparative Genomic Hybridization (CGH)

Comparative Genomic Hybridization (CGH) is a technique used to examine the genetic composition of embryos by analyzing all 23 pairs of chromosomes, including the 22 pairs of autosomes and the 1 pair of sex chromosomes. This method involves molecular-level genetic analysis using a technique called Whole Genome Amplification (WGA) to increase the amount of genetic material before testing. As a result, this technique provides more detailed information about the genetic status compared to standard chromosome-level testing. In general chromosome-level testing, specific genetic markers of interest and standard genetic markers are used with fluorescent probes that have different colors.  The samples are then subjected to hybridization and analyzed using computer programs. These programs can determine if the embryo has aneuploidy (missing or extra chromosomes), unbalanced translocations (abnormal chromosomal arrangements), or chromosome deletions or duplications (missing or duplicated portions of chromosomes).

However, this method has limitations in detecting certain types of chromosomal abnormalities, such as balanced translocations or inversions. This is because these abnormalities do not alter the overall quantity of genetic material compared to the standard reference. The testing process for these abnormalities using Next Generation Sequencing (NGS) can take approximately 24-72 hours, depending on the specific techniques employed.

In the human body, we have a total of 23 pairs of chromosomes, as mentioned earlier. Each chromosome plays a role in controlling various physical characteristics and functions of the body. Within the chromosomes, genes are composed of numerous base sequences, which in turn consist of amino acids. Genes that are abnormal or mutated can lead to the occurrence of diseases in individuals who inherit these gene abnormalities. The use of Next Generation Sequencing (NGS) technology in genetic testing allows for the detection of chromosomal abnormalities down to the base sequence level, which is the smallest component of a chromosome. By comparing the base sequences of disease-causing genes with normal genes, it becomes possible to identify the specific genes responsible for the disease. This method enables a detailed and highly accurate assessment of chromosomal abnormalities and has been developed and applied for genetic screening of embryos, making it the current state-of-the-art technique in genetic testing.

One advantage of using Next Generation Sequencing (NGS) technology for genetic testing is that it can detect abnormalities in all 24 chromosomes, providing highly detailed and highly accurate data with up to 99.9% accuracy. Furthermore, the testing process is faster, as the results can be obtained within 24 hours.

However, it’s important to note that Next Generation Sequencing technology is currently unable to detect diseases caused by single gene disorders, low-level mosaicism (a mixture of normal and abnormal cells), polyploidy (an abnormal number of sets of chromosomes), and small-scale deletions or duplications of chromosome segments that are smaller than the detection capability of the method, such as deletions or duplications smaller than 10 Mb.

Limitations of pre-implantation genetic diagnosis

Pre-implantation genetic testing still has limitations in terms of the accuracy of test results. Despite having high accuracy rates of up to 95-99%, it cannot replace the diagnostic accuracy of genetic testing before birth. Therefore, even if prenatal genetic testing has been performed, it is still recommended to undergo genetic testing before birth, similar to a natural pregnancy. Additionally, it is advisable for the couple to be informed about the chances of having a suitable fetus for transfer. In some cases, there may be limited chances of having a suitable fetus, such as in the screening for thalassemia combined with HLA compatibility testing for a child with a specific disease. Therefore, the couple may need to undergo multiple treatments before achieving a suitable fetus for pregnancy.

Genesis Fertility Center’s technology

The Genesis Fertility Center has selected a genetic testing technology that provides the most accurate and precise results of chromosomal analysis, with rapid results and minimal disruption to fetal development. This technology involves either extracting cells from the fetus or obtaining amniotic fluid during the blastocyst stage for genetic testing using Next Generation Sequencing. The results obtained from this testing method assist the physician in making decisions regarding which embryo to transfer into the uterus to maximize the chances of a successful pregnancy. Prenatal genetic testing before embryo transfer provides more information about fetal abnormalities, enabling healthcare professionals and couples undergoing treatment to make more informed decisions in embryo selection and transfer, thereby reducing the risk of transmitting genetic disorders and increasing the chances of a successful pregnancy.  Couples interested in embryo genetic testing should first determine if they have indications for testing. They will then receive an explanation of the testing technique, its limitations, result interpretation accuracy, testing success rates, embryo implantation success rates, and the associated costs before making a decision. In cases where pregnancy occurs, it is advisable for couples to consider pre-birth diagnostic testing to confirm the results of prenatal genetic analysis.