What Is PGT Testing? A Clear Guide to Embryo Screening in IVF

A laboratory dish holds five-day-old embryos, each no larger than a pinhead, as technicians prepare to analyze a few cells removed from what will become the placenta. The letters stand for preimplantation genetic testing, and the goal is to give your fertility team a closer look at each embryo’s chromosomes or specific genes before transfer.

Think of it as a quality filter at the very earliest stage of pregnancy, one that traditional prenatal screening simply cannot provide at this point.

This guide explains what PGT testing involves during IVF, breaks down its three categories, walks through how embryos are biopsied, and helps prospective parents weigh who benefits most.

Preimplantation Genetic Testing, Defined

The acronym PGT replaced two older terms, PGS (preimplantation genetic screening) and PGD (preimplantation genetic diagnosis), to reduce confusion around what each test actually looks for. The new naming system splits into three branches, PGT-A, PGT-M, and PGT-SR, so a clinic can tell you precisely which question the test is designed to answer.

The biopsy itself happens at the blastocyst stage, five or six days after fertilization, when the embryo has divided into hundreds of cells. A specialist removes five to seven cells from the trophectoderm, the outer layer that eventually forms the placenta. The inner cell mass that becomes the baby remains largely untouched, and the embryo is usually vitrified (a flash-freezing method) while the cells head to a genetics lab for analysis.

Quick glossary of terms

• ▸Blastocyst: A day-5 or day-6 embryo with a fluid-filled cavity and two distinct cell groups.
• ▸Trophectoderm: The outer cell layer of a blastocyst, the part sampled during PGT biopsy.
• ▸Inner cell mass: The cluster of cells inside the blastocyst that develops into the fetus.
• ▸Vitrification: Rapid freezing that preserves embryos for later transfer without forming ice crystals.
• ▸Aneuploidy: A chromosome count that is too high or too low, a leading cause of implantation failure and early miscarriage.

The Three Categories and What Each One Screens For

Each PGT branch solves a different problem, so the right choice depends on your reproductive history, your carrier screening results, and the specific condition you hope to avoid. Most clinics describe the three this way:

PGT-A for chromosome count

PGT-A counts the chromosomes in each embryo and flags any with an abnormal number, such as trisomy 21 (Down syndrome) or monosomy X (Turner syndrome). Because aneuploidy is the most common explanation for implantation failure and miscarriage, particularly in patients over 35, this is the PGT branch most fertility clinics recommend for age-related risk reduction.

Labs that run PGT-A include Natera, Igenomix, and CooperGenomics, all of which use next-generation sequencing (NGS) platforms for higher resolution than older FISH analysis.

PGT-M and PGT-SR for inherited conditions

PGT-M targets single-gene disorders that follow known inheritance patterns. Couples who are both carriers for cystic fibrosis, for example, can use PGT-M to identify embryos free of both disease-causing mutations. PGT-SR applies when one partner carries a balanced translocation or inversion that can produce embryos with broken or missing pieces of chromosomes; the test detects the unbalanced versions so the clinic can prioritize structurally normal embryos for transfer.

Knowing what each category looks for only matters once you understand how the lab actually gets its hands on the embryo in the first place.

Inside the Lab: How an Embryo Is Biopsied and Analyzed

The lab work runs on a tight clock that fits inside a single IVF cycle. Here’s how the timeline typically unfolds once eggs have been fertilized.

Day 5 to 6: Trophectoderm biopsy

Embryos grow in the incubator until they reach the blastocyst stage. An embryologist uses a laser or fine glass pipette to open the outer shell, then draws five to seven cells from the trophectoderm. The embryo is vitrified shortly after, while the biopsied cells go into a tube and are shipped (often on the same day) to a specialized genetics lab.

Day 7 to 14: Genetic analysis

At the lab, technicians amplify the DNA and run it through an NGS or PCR-based platform, depending on the test. PGT-A uses NGS to read chromosome counts across the whole genome. PGT-M usually relies on a custom PCR-based assay built around the family’s specific mutation.

Results generally arrive in seven to fourteen days, and your clinic receives a report listing each embryo as euploid (chromosomally normal), aneuploid (abnormal), or, in some cases, mosaic (a mix of normal and abnormal cells).

Scheduling the transfer

Because the biopsy and analysis take roughly two weeks, most clinics freeze all embryos and schedule the transfer in a later cycle. This frozen embryo transfer approach lets the uterus recover from stimulation medications and gives you time to review results with your care team before choosing which embryo to thaw.

Even with a clean biopsy, the results come with caveats that can reshape how confidently you trust a single report.

“Embryo damage from trophectoderm biopsy is rare at clinics with experienced embryologists, and the American Society for Reproductive Medicine (ASRM) considers the procedure safe when performed by trained hands. Confirm your clinic’s biopsy volume before committing to the cycle.

Accuracy, Mosaicism, and What PGT Cannot Promise

Misdiagnosis rates sit in a narrow band, often under one to two percent, but no genetic test is perfect. Three honest limits deserve your attention before you commit.

Mosaicism adds real uncertainty

Some embryos contain a mix of normal and abnormal cells, a finding called mosaicism. The biopsied trophectoderm may not fully represent the inner cell mass, so a mosaic result means the embryo’s true potential is uncertain. Many clinics still offer mosaic embryos for transfer after thorough counseling, and live births have resulted, but the decision involves more discussion than a clean euploid or aneuploid call.

PGT screens only what it is designed to detect

PGT-A cannot rule out autism, intellectual disability, birth defects caused by environmental exposures, or any of the thousands of rare single-gene disorders not included in the PGT-M assay. If your goal is a guarantee of a healthy baby, no embryo test can deliver that. Prenatal screening later in pregnancy, such as NIPT or amniocentesis, remains standard practice, especially for high-stakes indications.

False positives and negatives do happen

Lab quality, platform choice, and the specific indication all influence reliability. Some clinics publish their internal error rates; the Society for Assisted Reproductive Technology (SART) collects clinic-level outcomes that can help you compare programs. Ask your embryologist how often their lab has re-biopsied or recalled embryos, and what happens if a result comes back inconclusive.

Those accuracy limits become more or less consequential depending on who is sitting in the clinic chair.

Who Benefits Most and When the Test Makes Sense

PGT is not a universal add-on. The strongest case for testing shows up in a handful of well-defined situations.

Candidates with the clearest indication

• ▸Advanced maternal age: Aneuploidy risk climbs steeply after 35, and PGT-A helps identify the embryos most likely to implant.
• ▸Known monogenic disorders: Couples carrying cystic fibrosis, Huntington’s, or sickle cell disease often pursue PGT-M to break the inheritance chain.
• ▸Recurrent pregnancy loss: Three or more miscarriages frequently trace back to chromosomal errors that PGT-A can screen out.
• ▸Structural rearrangements: A partner with a balanced translocation benefits from PGT-SR to avoid unbalanced embryos.
• ▸Prior IVF failure: Patients with multiple failed transfers sometimes use PGT-A to rule out embryos that never had a realistic chance.

Cases where PGT is worth a longer conversation

Patients with a very small number of embryos may not want to risk losing any to a biopsy or inconclusive result. Single-embryo transfer candidates sometimes use PGT for added selection confidence, while others prefer to transfer without testing and let nature take its course. Donor gamete cycles produce embryos from younger donors, which can lower aneuploidy risk enough that some clinics recommend PGT less strongly.

Religious, ethical, or personal frameworks around embryo disposition also shape the choice, and a candid conversation with a genetic counselor often clarifies which trade-offs feel acceptable.

Cost, Trade-Offs, and the Decision to Test

The price tag is one of the first things couples ask about, and the honest answer depends on where you live, which insurer you carry, and what your clinic charges. Here is what the math usually looks like.

What you’ll likely pay

PGT typically adds several thousand dollars to an IVF cycle, on top of the cycle itself, medications, and embryo freezing. A single PGT-A biopsy can run anywhere from roughly $3,000 to $7,000 for a small batch of embryos, and PGT-M or PGT-SR assays are even more expensive because they require custom probe development.

Insurance coverage varies widely by state mandate, employer plan, and clinical indication, so the same test might be fully covered for one couple and entirely out-of-pocket for another.

Weighing cost against potential savings

The trade-off is not just dollars, it is also time, emotional energy, and the chance of avoiding a miscarriage or the birth of a child with a serious genetic condition. A failed transfer burns another cycle’s worth of medication and monitoring. A pregnancy loss costs months of grief. Some clinics report higher live birth rates per transfer with PGT-A in select age groups, though whether PGT improves cumulative outcomes across multiple cycles remains actively debated in the literature.

How to decide for your situation

Start by mapping your reproductive history, your carrier screening results, and your budget against the three PGT branches. Then book a joint consultation with a reproductive endocrinologist and a genetic counselor, the two professionals best equipped to translate test choice into a personal recommendation. Ask about clinic-specific error rates, mosaic embryo policies, and what happens if results come back inconclusive. Your clearest next step is a candid conversation grounded in your own numbers, values, and timeline.

Bottom Line

Your IVF team can peer into the genetic makeup of every embryo before transfer, but the three available branches (PGT-A, PGT-M, and PGT-SR) serve very different diagnostic purposes. The strongest candidates are patients of advanced maternal age, carriers of monogenic disorders, and couples facing structural rearrangements or repeated loss. The test cannot promise a healthy baby, but it can sharpen embryo selection in ways that traditional prenatal screening simply cannot.

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