The third-generation IVF technique, known as Preimplantation Genetic Testing [Preimplantation Genetic Diagnosis (PGD)/Preimplantation Genetic Screening (PGS)], involves analyzing the genetic material of gametes or embryos before implantation. This can be considered one of the earliest forms of prenatal diagnosis, aiming to detect any genetic abnormalities in the gametes or embryos.

Objective: To select embryos with normal test results for transfer.

When Is Third-Generation IVF (PGD/PGS) Recommended?

  • PGD (Preimplantation Genetic Diagnosis): For couples with a confirmed diagnosis of a genetic disorder or who carry pathogenic genes.
  • PGS (Preimplantation Genetic Screening): A screening method to select the best embryos.

PGD

1. Blocking Single-Gene Inherited Diseases:
Used when one partner has a known gene mutation-caused disease, both partners are carriers, or there is a family history of genetic disorders, such as dominant or recessive chromosomal genetic diseases.

2. Blocking Chromosomal Microdeletions:
Detectable diseases include (but are not limited to):

  • a. Cystic Fibrosis
  • b. Fragile X Syndrome
  • c. Huntington’s Disease; BRCA1/BRCA2 (e.g., hereditary breast/ovarian cancer)
  • d. Thalassemia
  • e. Spinal Muscular Atrophy (SMA)
  • f. Duchenne Muscular Dystrophy (DMD)
  • g. BRCA1/BRCA2 (e.g., hereditary breast/ovarian cancer)
  • h. DiGeorge Syndrome, chromosomal microdeletions related to spermatogenesis.

Tips:
BRCA1 is the breast cancer type 1 gene, and BRCA2 is the breast cancer type 2 gene.

PGS

PGS is another method for selecting the best embryos, screening for genetically and chromosomally normal embryos for transfer. In China, PGS cannot be used for selecting the gender of embryos. This technique is primarily used when either or both partners have chromosomal abnormalities (including numerical and structural abnormalities), such as aneuploidy, mosaicism, trisomy, chromosomal deletions, duplications, inversions, or translocations (both balanced and unbalanced, including Robertsonian translocations), or when testicular biopsy shows abnormal or mosaic karyotypes of germ cells.

When Can PGS Be Used?

  • Older female age in infertile couples (e.g., >35 years, though some believe a higher age threshold is necessary).
  • Male partner with X-linked genetic diseases or female partner as an X-linked genetic carrier; or one partner as a carrier of autosomal recessive diseases.
  • Multiple failed IVF/ICSI attempts.
  • Embryos that divide too rapidly.
  • Severe male infertility factors.
  • Patients with recurrent miscarriages.

How Is Genetic Testing Done?

1. Invasive Method:
“Embryo or Blastocyst Biopsy” — A process in which a small piece of developing embryo or blastocyst tissue is taken using a sharp, fine needle under a microscope for testing.

2. Non-Invasive Method:
The culture medium in which each embryo is grown is separately collected and preserved for testing. This medium is typically discarded as waste. This method does not harm the embryo at all, but it requires higher standards for collecting and testing the culture medium.