Genetics · MU Sofia

54. Preimplantation Genetic Tests.

Covers preimplantation genetic testing of IVF embryos and the prenatal tests that follow it, set out in that order. It explains the indications, the three forms of PGT (aneuploidy, monogenic disease and structural rearrangements) and the embryo biopsy stages, with a table comparing biopsy material and timing. Prenatal coverage includes non-invasive screening from maternal blood, invasive sampling methods, prenatal genetic analyses, indications, counselling and ethical aspects.

Inside: 9 sections · 8 labelled pictures · 1 table · 15 flashcards · 4 min

Topic 54 of 65 in the MU Sofia syllabus for Genetics (Medicine, Year 3). The free AceMed note covers it in 9 sections, about 485 words (4 min of reading), with 15 flashcards.

In this note

  1. Preimplantation Genetic Tests.
  2. PREIMPLANTATION GENETIC TESTING (PGT)
  3. Embryo Biopsy
  4. Types of Preimplantation Genetic Testing
  5. III. PRENATAL DIAGNOSIS AND PRENATAL GENETIC TESTING
  6. C. GENETIC ANALYSES IN PRENATAL DIAGNOSIS
  7. IV. INDICATIONS FOR PRENATAL GENETIC TESTING
  8. VI. GENETIC COUNSELING IN PRENATAL TESTING
  9. VII. ETHICAL AND PSYCHOSOCIAL ASPECTS

Preimplantation Genetic Tests.

Genetic testing can be divided into:

  1. 1. Preimplantation genetic testing (PGT) – before pregnancy is established
  2. 2. Prenatal genetic testing – during an established pregnancy

PREIMPLANTATION GENETIC TESTING (PGT)

Preimplantation genetic testing (PGT) refers to genetic analysis of embryos created by in vitro fertilization (IVF) before transfer into the uterus.

The goal is to select embryos without specific genetic abnormalities.

Indications for PGT

  • Known monogenic disease in one or both parents
  • Parental chromosomal rearrangements
  • Recurrent pregnancy loss
  • Advanced maternal age
  • Severe male factor infertility

Embryo Biopsy

Genetic material is obtained from the embryo without compromising its developmental potential.

Stages of Embryo Biopsy

Types of Preimplantation Genetic Testing

1. PGT-A (Preimplantation Genetic Testing for Aneuploidy)

Purpose

  • Detects numerical chromosomal abnormalities (aneuploidies).

Indications

  • Advanced maternal age
  • Recurrent implantation failure
  • Recurrent miscarriages

Pathogenesis addressed (in points)

  1. 1. Embryonic aneuploidy is common in IVF embryos.
  2. 2. Aneuploid embryos have low implantation potential.
  3. 3. PGT-A improves selection of euploid embryos.

2. PGT-M (Preimplantation Genetic Testing for Monogenic Disorders)

Purpose

  • Detects specific single-gene disorders.

Indications

  • Autosomal recessive, autosomal dominant, or X-linked diseases
  • Examples:
  • cystic fibrosis,
  • thalassemia,
  • Huntington disease.

3. PGT-SR (Preimplantation Genetic Testing for Structural Rearrangements)

Purpose

  • Detects unbalanced chromosomal rearrangements.

Indications

  • Parental balanced translocations or inversions

Genetic Methods Used in PGT

  • PCR-based techniques
  • FISH (older method)
  • Chromosomal microarray (aCGH)
  • Next-generation sequencing (NGS)

Advantages of PGT

  • Prevents implantation of affected embryos
  • Reduces miscarriage risk
  • Avoids need for pregnancy termination

Limitations of PGT

  • Mosaicism may cause false results
  • Cannot detect all genetic diseases
  • Requires IVF
  • Ethical considerations

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