With the advancement of sequencing technologies, genetic screening of embryos before implantation has emerged as a new technique combining genetics and human assisted reproductive technology. Known as “third-generation IVF,” it extends prenatal diagnosis, offering pre-implantation screening for patients with chromosomal diseases or monogenic disorders. This technology helps prevent the implantation of embryos with chromosomal or genetic abnormalities, effectively preventing the birth of children with genetic diseases. Commonly used are Preimplantation Genetic Screening (PGS) and Preimplantation Genetic Diagnosis (PGD), both of which can directly identify problematic embryos and select healthy ones for implantation, aiming to achieve normal pregnancies and increase clinical pregnancy rates. The primary difference between the two is that PGS is a screening technique, whereas PGD is a diagnostic tool, each targeting different groups and serving different purposes.

  1. Preimplantation Genetic Screening (PGS) PGS involves taking 1-2 cells from day-three embryos or 3-5 cells from the trophectoderm of day-five blastocysts for chromosomal number or structural screening using technologies such as FISH, aCGH, SNP, or NGS. This method serves as an early prenatal screening technique. By selecting normal embryos for uterine implantation, it aims to secure normal pregnancies, improve clinical pregnancy rates, and reduce the risks of multiple pregnancies.
    • Applicable Populations
      1. Women aged 35 and older
      2. Patients with recurrent miscarriages
      3. Individuals with multiple IVF failures (≥3 cycles)
      4. Patients with severe male infertility
    • Significance PGS technology increases the chances of pregnancy for infertile patients while also reducing the risks of miscarriage or giving birth to malformed fetuses.
    • Knowledge Expansion Normal chromosomal numbers and structures are crucial for the success rate of IVF. However, after embryo transfer, various factors such as the uterine environment, infections, diet, and living conditions can affect fetal development, potentially leading to chromosomal abnormalities and embryonic arrest. It’s noteworthy that even after successful conception through PGS, pregnant women still need to undergo routine prenatal testing.
  2. Preimplantation Genetic Diagnosis (PGD) PGD involves taking 1-2 cells from day-three embryos or 3-5 cells from the trophectoderm of day-five blastocysts and using technologies like FISH, aCGH, SNP, or NGS to screen for genetic mutations, selecting healthy embryos for implantation. This prevents couples from conceiving children with genetic abnormalities and ensures the birth of healthy offspring.
    • Applicable Populations
      1. Patients who have had to undergo abortions due to severe genetic issues
      2. Individuals who have conceived or have children with severe genetic problems
      3. Families with a history of severe genetic diseases
      4. Individuals with a family history of genetic disorders
      5. Patients with chromosomal translocations
    • Significance
      1. PGD can effectively prevent the birth of children with genetic diseases in older women and high-risk groups.
      2. It can avoid the risks and psychological burdens associated with traditional prenatal diagnostic techniques that treat abnormal embryos, mid-pregnancy genetic diagnosis, and pregnancy termination.
      3. It helps eliminate embryos carrying genetic diseases, preventing the transmission of pathogenic genes within the population and reducing the burden on families and society.

PGD is now used for specific diagnoses of common monogenic defects such as Duchenne Muscular Dystrophy, Fragile X Syndrome, Tay-Sachs Disease, Cystic Fibrosis, Rh blood type, Hemophilia A, Sickle Cell Anemia, Thalassemia, Neonatal Hemolysis, 21-hydroxylase Deficiency, Mucopolysaccharidosis, and Werdnig-Hoffmann Disease.