Embryo screening: the complete map for IVF families
Most IVF families learn about embryo screening backwards. Your clinic mentions PGT-A. Maybe a counselor brings up PGT-M. And if you've done enough late-night reading, you might've stumbled across PGT-P. But nobody sits you down and shows you how all of these fit together, what each one actually tests for, or what falls through the cracks when you only do one.
Here's the problem: PGT-A, the test nearly every clinic offers, screens for the rarest category of problems. The common diseases that actually run in families (diabetes, heart disease, Alzheimer's, breast cancer) require a completely different test that most clinics never mention. Families end up making transfer decisions with a fraction of the genetic information that's actually available to them.
The test your clinic recommends and the gap it leaves
Embryo screening is genetic testing done on embryos during IVF, before a transfer. The process starts the same way regardless of which test you're doing. On day 5 or 6, when an embryo has developed into a blastocyst, an embryologist takes a small biopsy from the trophectoderm, the outer layer of cells that will eventually become the placenta, not the baby. That's roughly 5 to 10 cells. They're sent to a genetics lab, the DNA is extracted and analyzed, and the results tell you different things depending on which test was run.
When your clinic says "genetic testing," they almost always mean PGT-A: preimplantation genetic testing for aneuploidy. It checks whether each embryo has the right number of chromosomes. Humans are supposed to have 46, 23 from each parent. An embryo with too many or too few is aneuploid, which can lead to failed implantation, miscarriage, or chromosomal conditions like Down syndrome. The older the eggs, the more common aneuploidy becomes.
The scale is bigger than most people realize. One in every 37 babies born in the US in 2022 was conceived through assisted reproductive technology. That's over 435,000 ART cycles on roughly 252,000 patients in a single year. And PGT-A has grown fast within that. In 2014, only about 17% of US IVF cycles included it. By 2020, roughly 49%. That growth happened because the test answered a question clinics cared about: which embryos are most likely to implant?
But here's what PGT-A doesn't tell you: anything about disease risk.
An embryo can have a perfectly normal chromosome count and still carry a high genetic predisposition for common diseases like type 2 diabetes. Euploid just means the chromosome count is right. It tells you nothing about the hundreds of individual genetic variants that influence whether someone develops a chronic condition later in life.
Families who stop at PGT-A often assume they've done all the screening that's available.
They haven't.
What single-gene testing can and can't see
There's a second type of testing that's been around for decades. PGT-M (preimplantation genetic testing for monogenic disorders) looks for specific single-gene conditions. Both parents do carrier screening first. If that screening reveals they both carry a variant for something like cystic fibrosis or spinal muscular atrophy, PGT-M can identify which embryos inherited the disease-causing variants and which didn't. SMA alone is the leading genetic cause of infant death, with a carrier frequency of about 1 in 40 to 1 in 60.
This is settled science. In countries where carrier screening and IVF were made widely accessible for cystic fibrosis carriers, the prevalence of the disease among newborns declined by over 90%.
That was a huge victory for public health. But it only worked for conditions caused by a single gene.
ACMG now recommends carrier screening for conditions like cystic fibrosis and SMA regardless of ethnicity. That's a positive shift. Carrier screening used to be based on your ethnic background, and that approach missed people. But a couple who screens out a cystic fibrosis variant still doesn't know anything about their embryos' risk for the common diseases most families worry about. Those are shaped by hundreds of genetic variants each. A single-gene test can't see them.
The diseases that actually run in families
The conditions that fill most hospital beds and the ones most families worry about when they think about their children's health aren't caused by a single gene or a wrong chromosome count. Type 2 diabetes, heart disease, Alzheimer's, schizophrenia, breast cancer: these are polygenic, influenced by many genetic variants, each contributing a small amount of risk that adds up differently in each person. Where cystic fibrosis traces back to variants in a single gene, type 2 diabetes involves hundreds.
For a long time, there was no way to screen embryos for these conditions.
PGT-P changes that. Preimplantation genetic testing for polygenic conditions identifies which embryos inherited a more favorable genetic hand and which ones didn't. Sometimes a child gets an unlucky combination and ends up with many high-risk variants from both parents. PGT-P can tell you which embryos carry that higher risk before you decide which one to transfer.
Most IVF patients never hear about PGT-P because their clinics don't offer it. But the science behind it is real, and for families with a history of common diseases, it's a layer of information that chromosome counting and single-gene testing simply can't provide.
Think about what this means in practice. A couple going through IVF might have five euploid embryos. PGT-A says all five are chromosomally normal. PGT-M says none carry the cystic fibrosis variant both parents carry. From the clinic's perspective, all five look equally good. But one of those embryos might carry a 23% genetic predisposition for type 2 diabetes while another sits at 3.5%. Without PGT-P, there's no way to know. That's not a rounding error. That's a different life trajectory.
Three tests, three completely different types of genetic information, and most families only ever hear about the first one.
These risk numbers aren't all-or-nothing. A 25% risk of type 2 diabetes means something different depending on your family. For families where both parents have diabetes, that might actually be a good outcome. For a family with no history, the same number is concerning. The line between "has the disease" and "doesn't" is blurrier than a single percentage suggests, which is why Herasight's counselors walk families through what the results mean for your specific situation, incorporating family history so the numbers actually connect to your life.
How we know the scores work
How do you know these scores actually predict anything for embryos?
It's the right question. And the answer depends on something specific to the IVF context that most people don't think about.
Embryos from the same cycle are siblings. They share the same parents and the same ancestry. A polygenic score that works well at the population level (distinguishing unrelated strangers) can lose its edge when you narrow the comparison to siblings who share half their DNA. So the only validation that matters here is within-family prediction: do the scores still tell siblings apart?
We tested 17 disease scores on sibling pairs. 16 out of 17 held up with no decrease in predictive performance within families.
That's not a technicality. It's the whole point. If a score can't differentiate siblings, it's useless for embryo screening. Ours can.
We also built these scores specifically for the embryo context rather than licensing off-the-shelf academic models designed for adult populations. The result: 28 to 193% higher accuracy in within-family comparisons.
And for families who've already done PGT-A at another clinic: you may not need a new biopsy.
Standard PGT-A captures a thin layer of genomic data. Not much, but not nothing. Our ImputePGTA technology can take that existing data and combine it with high-quality parental sequencing to reconstruct a full embryo genome. No additional biopsy. No additional risk to the embryo. If you've already been through a PGT-A cycle, the data you need for polygenic screening may already exist.
Where this is heading
PGT-A went from 17% of US IVF cycles in 2014 to roughly 49% by 2020. Six years. When a genetic test proves useful, adoption moves fast.
PGT-P is at the beginning of that same curve. Most IVF patients don't know it exists. Most clinics don't mention it. But the same was true of PGT-A a decade ago.
The gap between what's technically possible and what most clinics offer is wide. Early polygenic scores only worked well for people of European descent. That's changed. Scores now work across 8+ ancestry groups. Family history, one of the strongest predictors of disease risk, is now integrated into scoring rather than ignored. And the practical barriers keep falling: families who've already done PGT-A don't need a second biopsy, and the cost and timeline are becoming more manageable as the technology matures.
Most fertility clinics still treat PGT-A as the ceiling of embryo screening. It isn't. The science has moved past it, and the ethical framework for responsible use is already well-developed. The underlying question for families is simpler than the technology: if you could know more about your embryos' health risks before choosing which one to transfer, would you want to?
We think most people would say yes.
Where to go from here
If this is your first encounter with polygenic screening, the PGT-P deep dive covers the history, the mechanism, and what makes within-family validation different from population-level studies. The type 2 diabetes article walks through the genetics and risk spread for a specific condition with real numbers.
For the decision itself: the decision guide helps you think through the factors that matter. The article on what Herasight's counselors do explains how interpretation works and why it matters that the people reading your report understand polygenic scores deeply.
For practical questions: how much PGT costs and how long results take. The expected gains calculator shows what screening could look like with your embryo count, and the IVF calculator helps you model outcomes across your full cycle.
If you want to talk through the options, reach out to our team.
Herasight provides polygenic embryo screening for IVF families. We do not provide medical diagnoses or advice on which embryo to transfer. Screening results are risk estimates, not guarantees. All transfer decisions should be made in consultation with your physician.