Unit
- Definition and purpose: Preimplantation genetic testing (PGT) involves analyzing embryos created through in vitro fertilization (IVF) for genetic abnormalities before transfer to the uterus. The primary objective is to identify embryos with a lower risk of genetic disorders, thereby improving the chances of a healthy pregnancy.
- Historical development: PGT emerged in the late 1980s as a practical application of advances in molecular genetics and assisted reproductive technology. The first successful PGT cycle occurred in 1990, leading to the birth of a child free from a sex-linked disorder. Since then, techniques have evolved from polymerase chain reaction (PCR) to comprehensive chromosomal screening.
- Types of PGT: Three main categories exist: PGT for aneuploidy (PGT-A), which screens for chromosomal number abnormalities; PGT for monogenic disorders (PGT-M), which detects specific single-gene mutations; and PGT for structural rearrangements (PGT-SR), which identifies chromosomal structural changes such as translocations.
- Role in IVF: PGT is performed on embryos created through IVF, typically at the blastocyst stage (day 5 or 6 of development). A small number of cells are removed from the trophectoderm (the outer layer that forms the placenta) and analyzed, while the embryo remains intact and can be cryopreserved.
- Indications for PGT: Common indications include advanced maternal age, recurrent pregnancy loss, previous aneuploid pregnancy, known parental chromosomal rearrangements, and family history of a monogenic disorder. Couples may also choose PGT to reduce the risk of passing on a genetic condition.
- Ethical considerations: PGT raises ethical questions regarding embryo selection, potential for non-medical trait selection, and disposal of affected embryos. Regulatory frameworks vary worldwide, and genetic counseling is essential to ensure informed decision-making.
- Success rates and limitations: PGT can reduce the risk of miscarriage and increase the efficiency of IVF by allowing transfer of chromosomally normal embryos. However, it is not 100% accurate due to mosaicism, technical errors, or limited cell samples. Embryo biopsy also carries a small risk of damage.
- Multidisciplinary team: Successful PGT requires collaboration among reproductive endocrinologists, genetic counselors, embryologists, molecular geneticists, and laboratory personnel. Each professional contributes distinct expertise to the workflow from patient selection to result reporting.
- Biopsy techniques: Trophectoderm biopsy is the standard method for cell removal, involving laser assisted or mechanical dissection of 5 to 10 cells from the outer layer of the blastocyst. This technique minimizes embryo stress compared to earlier cleavage stage biopsy and allows for comprehensive analysis of multiple cells, improving diagnostic accuracy.
- Genetic analysis methods: Next generation sequencing (NGS) is the predominant technology used in PGT, offering high throughput and sensitivity for detecting aneuploidy, structural rearrangements, and monogenic disorders. NGS allows simultaneous screening for multiple conditions from a single biopsy sample, enhancing the efficiency and scope of testing.
Scope of Practice
Role: Preimplantation Genetics Laboratory Manager
Within scope:
- Overseeing the workflow from biopsy to genetic analysis
- Ensuring laboratory quality control and adherence to protocols
- Coordinating with IVF clinic staff for sample handling and timing
- Reviewing and validating genetic test results before reporting
- Managing laboratory personnel training and competency assessment
Outside scope:
- Performing embryo biopsy procedures (requires embryology team)
- Making decisions on which embryos to transfer (clinical team responsibility)
- Providing genetic counseling directly to patients (genetic counselor role)
- Interpreting clinical significance of genetic variants for treatment (clinical geneticist)
- Altering IVF stimulation protocols (reproductive endocrinologist)
Quick Revision
- PGT analyzes embryos for genetic abnormalities before IVF transfer.
- Three main types: PGT-A, PGT-M, PGT-SR.
- Indications include advanced maternal age, recurrent loss, known genetic risks.
- Limitations include mosaicism and technical error.
- Multidisciplinary team approach is essential.
Disclaimer
Educational use only. Not intended for practical surgery, incisions, or other surgical procedures. It does not qualify you to perform physical operations.