Preimplantation Genetic Testing (PGT): PGT-A, PGT-M and PGT-SR

What is preimplantation genetic testing?

Preimplantation genetic testing (PGT) is a laboratory technique used with IVF. When embryos reach the blastocyst stage, usually around day five or six, an embryologist removes a few cells from the part that will form the placenta, called the trophectoderm. The cells are sent to a genetic laboratory for analysis, and the embryo is frozen while the results are processed. Only embryos that meet the chosen criteria are then selected for transfer in a later frozen cycle.

PGT can only be done with IVF, because it requires embryos created in the laboratory. It does not apply to pregnancies from IUI or natural conception.

The three main types

PGT-A: aneuploidy screening

Most human embryos with the wrong number of chromosomes do not implant, or result in miscarriage. Because chromosome errors become more common with age, PGT-A aims to identify embryos with a normal number of chromosomes (euploid). The idea is to transfer the embryos most likely to lead to a healthy pregnancy and avoid losing time with those that will not.

PGT-M: monogenic or single-gene conditions

PGT-M is used when one or both parents carry a gene for an inherited condition, such as cystic fibrosis, sickle cell disease or Huntington disease. A lab develops a test specific to your family’s variant, and embryos without the condition can be selected. It often requires planning and time to set up the test.

PGT-SR: structural rearrangements

When a parent carries a balanced chromosome rearrangement, such as a translocation, embryos can inherit an unbalanced version, which often causes miscarriage or a child with health problems. PGT-SR identifies embryos with balanced or normal chromosomes.

Who may benefit

• Couples with a known inherited condition (PGT-M) or chromosome rearrangement (PGT-SR), for whom the benefit is well established
• People with recurrent pregnancy loss in selected situations. See recurrent pregnancy loss
• Older patients, in whom aneuploidy is more common, though evidence of improved live birth rates is debated
• People who want to limit the number of transfers or reduce the chance of miscarriage
• Some who want to avoid transferring more than one embryo and want information to choose

What PGT cannot do

• It cannot guarantee a baby. Even a euploid embryo may not implant.
• It does not test for every condition. PGT-A looks at chromosome number, not at every gene or developmental issue, and is not a replacement for prenatal screening and diagnosis.
• It cannot make embryos better. It only helps select among those that exist, and if none are normal, no transfer may be possible.

Accuracy and mosaic results

The test analyzes a small biopsy, which may not perfectly represent the whole embryo. False positives and false negatives are possible. Some embryos show a mix of normal and abnormal cells, called mosaic. How to handle mosaic embryos is debated: some clinics discard them, while others offer transfer after counseling because some have resulted in healthy births. Ask how your clinic interprets and counsels about mosaic results, and who within the lab performs the biopsy.

What the evidence says about PGT-A

Studies show different results. Some report higher implantation or lower miscarriage rates per transfer with PGT-A, particularly in older patients, while large randomized trials in general populations have not found improvement in cumulative live birth rates per egg retrieval, and some have suggested that testing may lead to discarding embryos that could have resulted in a baby. Professional societies describe the evidence as insufficient to recommend PGT-A for all patients. It remains widely offered, so it is important to ask what benefit you can expect in your own case, and not to assume it is standard or necessary.

Cost and logistics

PGT adds fees for biopsy, testing and sometimes embryo freezing, typically per embryo. Costs can be substantial, so ask for an itemized estimate. PGT-M may involve an additional set-up fee. Insurance coverage is variable. See fertility costs and insurance and use the IVF cost estimator.

Sex selection and ethical issues

PGT can reveal the sex of an embryo, and some clinics offer sex selection where legal. Policies differ between countries and between clinics, and professional societies have varying positions. Testing for non-medical traits raises ethical questions. Be sure that you understand your clinic’s policies and what laws apply.

Questions to ask

• Do you recommend PGT for me, and why?
• What type of testing, and what do you expect to gain?
• What is the accuracy, and how do you handle mosaic results?
• What is the cost per embryo, and what is included?
• How many embryos might I need to bank to get a normal result?
• Do you use an in-house lab or an outside lab, and how experienced is it?

Bring the list to your consultation using the appointment questions planner. Learn more about related options in ICSI and donor egg, sperm and embryo.