Embryo screening is three different tests, and most families only hear about one

Most IVF patients hear "your embryos were tested" and assume that covers everything. It almost never does.

Embryo screening isn't one test. It's three, and each one answers a fundamentally different genetic question. One counts chromosomes. One looks for specific inherited mutations like cystic fibrosis. And the third measures the combined effect of hundreds of genetic variants on common disease risk.

Most families going through IVF are only offered the first. The test that screens for the conditions most families actually carry (type 2 diabetes, heart disease, breast cancer, Alzheimer's) is one most patients are never told exists.

If you're interested in learning more about what embryo screening can tell you, you can reach out to us here.

What the default test does (and what it misses)

The test most clinics offer is called PGT-A. It checks whether each embryo has the right number of chromosomes: 46, arranged in 23 pairs. An embryo missing a chromosome or carrying an extra one usually won't implant or will end in miscarriage, so this is genuinely useful information.

But a "normal" PGT-A result doesn't mean what many families think it means. It means the chromosome count looks right. That's it. A euploid embryo can still carry significant genetic risk factors for the diseases that actually fill hospital beds: diabetes, heart disease, Alzheimer's. PGT-A simply can't see them.

There's a second test, PGT-M, that screens for specific single-gene conditions like cystic fibrosis or sickle cell disease. In countries where carrier screening and IVF were made available for cystic fibrosis carriers, the prevalence of the disease among newborns declined by over 90%.

That was a huge victory for public health.

But most diseases still remained out of reach. Conditions like diabetes, Alzheimer's, and heart disease aren't caused by a single mutation. They're influenced by hundreds of genetic variants, each contributing a small amount of risk. Until recently, there was no way to measure that combined effect in an embryo.

The variation most families never see

Every time two embryos are created from the same parents, the hundreds of risk variants each parent carries get shuffled and dealt differently. Think of it like a genetic roll of the dice. Two embryos from the same IVF cycle can end up with very different risk profiles, even though they share the same parents.

Polygenic preimplantation genetic testing (PGT-P) measures that variation. And the numbers are bigger than most people expect.

For type 2 diabetes, we've seen sibling embryos range from 3.5% to 23.3% lifetime risk. For hypertension, 12.2% to 45.3%. These aren't hypothetical numbers. They come from actual families we've worked with. And standard screening never measures any of it. A PGT-A result of "normal" tells you nothing about which embryo carries a 3.5% diabetes risk and which carries a 23.3% risk.

The testing itself is straightforward. During IVF, a small number of cells are taken from the outer layer of the embryo (the part that becomes the placenta, not the baby). A meta-analysis of over 31,000 live births found no association between trophectoderm biopsy and worse pregnancy or neonatal outcomes. The DNA from those cells gets sequenced, and each embryo gets a risk profile across multiple conditions.

If you want to understand what this kind of screening could mean for your embryos, our counselors can walk you through it.

We tested this on siblings, because that's what actually matters

Polygenic scores come from studies of large populations. A reasonable person might wonder: do they still hold up when you're comparing embryos from the same two parents? Siblings share parents, they share environment. If the scores were just picking up population-level noise rather than real genetic differences, they'd fall apart within families.

So we tested it directly. We validated 17 disease scores on sibling pairs, because that's the actual context of embryo screening: choosing among embryos from the same two parents. Sixteen out of seventeen scores showed no decrease in predictive performance within families. The scores work because they're capturing real genetic variation, not statistical artifacts.

This matters because nature has essentially run a randomized trial for us. Every time two siblings are created, the genes they inherit from each parent are shuffled and randomly assigned. That's what makes within-family validation so powerful: it tests whether the scores can identify real genetic differences between embryos that share the same parents and the same environment.

What this means if you've already done PGT-A

If your clinic told you your embryos are "normal," that's genuinely good news about their chromosomes. But it's not the whole story. The diseases that affect most people in the long run, the ones with strong genetic components that run in families, require a different kind of test to see. And the genetic variation between your embryos for those conditions is already there, whether anyone measures it or not.

The variation between your embryos is real, measurable, and often larger than most families expect. Roughly 2.6% of all U.S. infants are now born through assisted reproductive technology, and every one of those families deserves to know what information is available to them. Understanding which questions matter for your family is the first step toward a more complete picture of embryo screening.

One of our counselors can help you figure out whether this kind of screening makes sense for your situation. If you want to learn what embryo screening can tell you about your specific embryos, please reach out to us.