PGT: Preimplantation Genetic Testing Explained

What Is PGT and What Does It Actually Test?

Preimplantation genetic testing, or PGT, is a set of laboratory techniques used to examine the genetic makeup of embryos created during in vitro fertilization, before any embryo is placed in the uterus. The goal is straightforward: to gather more information about each embryo so that the one with the best chance of leading to a healthy pregnancy can be chosen for transfer. PGT is always paired with IVF, because the embryos must be created and grown in the laboratory in order to be tested.

It helps to understand what PGT does not do. It is not a fertility treatment in itself and it does not improve the quality of an embryo; it is a screening and diagnostic tool that gives you and your specialist a clearer picture of what is already there. Think of it as reading information that the embryo already carries, rather than changing anything about the embryo.

Because the science can feel overwhelming, it is normal to have questions and even mixed feelings. A good fertility team will explain your options in plain language and never pressure you toward testing you do not want. If you are still learning the basics, our guide to the IVF process walks through each stage, and our overview of fertility treatment in Colombia explains the wider range of care available to international patients.

The Three Types: PGT-A, PGT-M and PGT-SR

PGT is not one single test but a family of tests, each answering a different question. Knowing which one applies to you is the first step, and your genetic counselor will help determine that based on your history.

PGT-A tests for aneuploidy, meaning an abnormal number of chromosomes. Healthy embryos normally have 46 chromosomes; an embryo with a missing or extra chromosome is described as aneuploid. Such embryos are a common cause of failed implantation and miscarriage, and most cannot result in a healthy baby. PGT-A is the most frequently requested form of testing, often considered when age or pregnancy history raises the chance of chromosome errors.

PGT-M tests for a specific monogenic, or single-gene, disorder. It is used when one or both parents are known to carry a particular inherited condition, such as cystic fibrosis or sickle cell disease, and they wish to avoid passing it to their child. PGT-M is highly targeted and requires careful preparation in advance, because the laboratory must first design a test specific to your family's genetic variant.

PGT-SR tests for structural rearrangements of the chromosomes, such as translocations, where pieces of chromosomes are positioned differently than usual. A parent who carries a balanced rearrangement is usually healthy but may produce embryos with too much or too little genetic material. PGT-SR helps identify the embryos with the correct balance.

How PGT Fits Into the IVF Process

PGT is woven into a standard IVF cycle, with a few additional steps. Your treatment begins as any IVF cycle would: ovarian stimulation with medication, egg retrieval, and fertilization of the eggs in the laboratory, typically through a technique that injects a single sperm into each egg. From there, the fertilized eggs are cultured for several days so the embryologist can watch them develop.

The testing itself happens at the blastocyst stage, around day five or six, when a healthy embryo has grown to roughly two hundred cells. A skilled embryologist performs a biopsy, gently removing a few cells from the outer layer that would normally go on to form the placenta, not the baby itself. These cells are sent to a specialized genetics laboratory for analysis, while the embryos are carefully frozen, a process called vitrification, to await the results.

This is why a PGT cycle almost always involves a frozen embryo transfer rather than a fresh one. Results commonly take a couple of weeks, so the transfer happens in a later cycle once the report is ready and your specialist has reviewed it with you. Coordinating these stages across borders takes planning, which is one reason a facilitator can be helpful; you can read more about how we support patients on the HealthBridge home page.

Who May Benefit From PGT?

PGT is not recommended for everyone, and a thoughtful specialist will help you decide whether it is likely to add value in your particular situation. Several groups, however, are commonly considered candidates.

Women of advanced maternal age are often counseled about PGT-A, because the chance of chromosome errors in eggs rises naturally with age. For these patients, testing can reduce the number of transfers that fail or end in early miscarriage by helping to identify a chromosomally normal embryo. Couples who have experienced recurrent pregnancy loss may also benefit, since chromosome abnormalities are a frequent cause of miscarriage, and understanding the embryos can bring both clinical insight and emotional clarity.

Those who have been through repeated IVF cycles without success sometimes turn to PGT-A to refine embryo selection. Families with a known inherited condition are the clearest candidates for PGT-M, and individuals who carry a chromosomal rearrangement are candidates for PGT-SR. In every case, a genetic counselor is an essential part of the team, helping you understand your specific risk, what the test can realistically tell you, and what it cannot.

Honest Benefits and Real Limitations

It is important to talk about PGT honestly, because it is sometimes presented as more certain than it is. The genuine benefit is better-informed embryo selection. By prioritizing embryos that test as chromosomally normal, many patients can reduce the emotional and physical toll of failed transfers and miscarriages, and for families with a known genetic disorder, PGT-M can offer real reassurance about a specific condition.

The honest limitations matter just as much. PGT is not a guarantee of pregnancy; a normal-testing embryo still has to implant and develop. It does not screen for every possible genetic or developmental condition, only for what each specific test is designed to detect. Because the biopsy samples a small number of cells, there is a small possibility of an inconclusive or, rarely, an inaccurate result, and a phenomenon called mosaicism, where an embryo contains both normal and abnormal cells, can make interpretation more nuanced. Some cycles also produce no embryos suitable for testing or transfer, which can be painful to face.

There are practical and ethical dimensions too. PGT adds cost on top of IVF, and decisions about what to do with embryos involve deeply personal values that deserve unhurried reflection. A responsible team presents all of this clearly so your choice is truly your own. Our article on IVF cost can help you understand the financial side as you weigh whether to add testing.

Coordinating PGT for International Patients

For patients traveling from abroad, PGT requires extra coordination because the cycle unfolds in stages that do not all happen on the same trip. The retrieval, fertilization, embryo culture and biopsy take place during your time in Medellin, but the laboratory analysis and the eventual frozen embryo transfer typically occur weeks later. Planning this timeline carefully, around your travel and your body's cycle, is essential, and it is exactly the kind of logistics a facilitator helps manage.

HealthBridge is a facilitator, not a clinic. We connect you with board-certified fertility specialists, experienced embryologists and qualified genetic counselors, and we help arrange the consultations, scheduling and communication that an international PGT cycle demands. Dra. Olga Gonzalez serves as our medical director and coordinator, guiding you in clear language so you understand each step, including when you will need to travel and what to expect between visits.

Medellin offers modern accredited facilities, a mild spring-like climate and convenient flight connections from several U.S. cities, along with bilingual support throughout your journey. For couples facing the genetic side of fertility, the most reassuring thing is not a promise of a perfect outcome, which no honest provider can make, but a knowledgeable team that explains the science, respects your values and stands beside you through a process that is as emotional as it is medical.