Intro
Preimplantation genetic testing (PGT), previously referred to as preimplantation genetic diagnosis (PGD), is an advanced laboratory technique used in conjunction with IVF to evaluate embryos for genetic or chromosomal abnormalities before they are transferred to the uterus.
This article provides an in-depth explanation of PGT/PGD, including why genetic testing is performed, the different types of testing, how embryos are biopsied and analyzed, indications, limitations, risks, legal considerations, and factors influencing success.
What is PGT / PGD?
PGT is a genetic screening or diagnostic process performed on embryos created through IVF or IVF with ICSI.
The aim is to identify embryos with normal chromosomal structure or without specific genetic diseases before implantation, thereby improving the chance of a healthy pregnancy.
The term PGD is traditionally used when testing for known inherited genetic conditions, while PGT is now used as the umbrella term covering all types of embryo genetic testing.
Why genetic testing of embryos is performed
Not all embryos created through IVF are genetically normal. Chromosomal abnormalities are a leading cause of implantation failure, miscarriage, and certain congenital conditions.
PGT allows clinicians to select embryos with the highest potential for successful implantation and healthy development.
Main types of PGT
PGT-A (Aneuploidy screening)
PGT-A screens embryos for abnormal numbers of chromosomes.
Chromosomal aneuploidy is more common with increasing maternal age and is a major cause of failed IVF cycles and miscarriage.
PGT-A helps identify embryos with the correct number of chromosomes, improving implantation rates and reducing miscarriage risk in selected patients.
PGT-M (Monogenic disease testing)
PGT-M is used when one or both partners carry a known genetic mutation that could be passed on to the child.
This form of testing identifies embryos affected by specific inherited diseases such as cystic fibrosis, thalassemia, or certain metabolic disorders.
PGT-SR (Structural rearrangements)
PGT-SR is used when one partner carries a chromosomal structural rearrangement, such as a translocation or inversion.
These rearrangements may not affect the carrier’s health but can lead to repeated miscarriages or failed implantation.
How PGT is performed
IVF and embryo development
PGT can only be performed on embryos created through IVF or IVF with ICSI.
Embryos are cultured in the laboratory until they reach the blastocyst stage, typically on day 5 or 6 of development.
Embryo biopsy
A small number of cells are carefully removed from the outer layer of the blastocyst, known as the trophectoderm.
This layer later forms the placenta, while the inner cell mass develops into the fetus.
The biopsy process is performed using micromanipulation and laser technology and does not significantly compromise embryo viability when performed by experienced embryologists.
Embryo freezing after biopsy
Following biopsy, embryos are frozen using vitrification while genetic analysis is performed.
Embryo transfer is scheduled in a later frozen embryo transfer (FET) cycle.
Genetic analysis
The biopsied cells are analyzed using advanced genetic techniques such as next-generation sequencing (NGS).
Results typically categorize embryos as genetically normal, abnormal, or in some cases mosaic.
Legal and ethical considerations in Turkey
PGT is legally permitted in Turkey when performed for medical indications.
Testing is allowed to prevent serious genetic diseases or identify chromosomal abnormalities that may compromise pregnancy outcomes.
Non-medical sex selection and testing for non-health-related traits are prohibited.
PGT is only available to married couples using their own eggs and sperm.
Who may benefit from PGT?
PGT may be recommended for couples with:
- Advanced maternal age
- Recurrent pregnancy loss
- Repeated IVF implantation failure
- Known inherited genetic conditions
- Chromosomal rearrangements
Who may not benefit from PGT?
PGT may offer limited benefit when:
- A small number of embryos are available
- Egg quality is severely compromised
- Infertility is unrelated to genetic factors
Limitations of PGT
While PGT is a powerful tool, it has limitations.
Not all genetic conditions can be detected, and results depend on embryo quality and testing accuracy.
Mosaic embryos may present complex decision-making scenarios requiring genetic counseling.
Risks associated with PGT
PGT is considered safe, but potential considerations include:
- Embryo loss during biopsy or freezing (rare)
- False-positive or false-negative results (uncommon)
- Cycle cancellation if no transferable embryos are identified
Success factors in PGT cycles
Success depends on multiple factors:
- Female age at egg retrieval
- Number of embryos available for testing
- Laboratory expertise
- Underlying infertility diagnosis
PGT for international patients
PGT is frequently used by international patients undergoing IVF in Turkey.
Embryo freezing allows patients to return home while awaiting results and schedule a frozen embryo transfer at a later date.
Frequently asked questions
Does PGT guarantee a healthy baby?
No. PGT reduces certain genetic risks but cannot guarantee a successful pregnancy or a healthy child.
Can all embryos be tested?
Only embryos that reach the blastocyst stage and are suitable for biopsy can be tested.
Is PGT mandatory for IVF?
No. PGT is optional and recommended only when clinically indicated.
Important medical disclaimer
This content is provided for informational purposes only and does not replace a professional medical consultation. Treatment plans, suitability, techniques, and outcomes vary per patient and are determined by a licensed medical professional following an individual assessment.