Designer Babies: The Reality and Myths of Genetic Optimization in Embryos

In June 2025, a genomics company called Nucleus Genomics launched a product with a science-fiction premise and a real-world price tag. For around $5,999, Nucleus Embryo promised to help parents rank their IVF embryos by predicted intelligence, longevity, disease resistance, body mass index, eye colour and even left-handedness.

The pitch was control over a child’s biological future. The reality, as the peer-reviewed evidence shows, is considerably smaller than that promise implies.

The dream of choosing a child’s traits is old, running from Plato’s Republic to Huxley’s Brave New World to the film GATTACA. What is new is a company selling it as a subscription.

The gap between what the marketing implies and what the peer-reviewed science actually supports is where this whole story lives, and it is wider than the price tag suggests.

This article separates reality from hype. It explains what embryo screening genuinely does, why predicting complex traits from embryo DNA is far weaker than advertised, how small the real gains are once you read the studies, and why the ethics matter regardless.

What Preimplantation Genetic Testing Actually Does

The technology at the core of embryo screening is preimplantation genetic testing, or PGT. It is a well-established part of IVF, used for decades to check embryos for chromosomal errors and specific inherited mutations before one is transferred to the womb.

PGT works by taking a tiny biopsy from an embryo at the blastocyst stage, around five to six days after fertilisation. The embryo then has roughly 80 to 200 cells, and only about five are removed. The results show which embryos do not carry a targeted mutation.

In its most established form, testing for monogenic conditions (PGT-M), the technology is genuinely powerful. It flags embryos carrying single-gene mutations with clear effects: cystic fibrosis, sickle cell disease, Huntington’s disease, Tay–Sachs, and the BRCA1 and BRCA2 cancer-risk mutations.

For a family with a known inherited condition, PGT-M offers something profound and legitimate: the chance of a biological child free from that specific disease. The UK regulator has approved well over a thousand conditions for this kind of testing.

This connects directly to the wider science of inherited disease covered in our guide to the genetics of cancer.

Testing for aneuploidies (PGT-A) instead screens for the wrong number of chromosomes, a major cause of failed implantation and miscarriage. Its clinical value, however, is genuinely contested rather than settled.

The distinction matters. PGT-M answers a precise yes-or-no question about a single well-understood gene. Trait prediction asks something far harder: to forecast an outcome shaped by thousands of variants and a lifetime of environment. Only the first is on solid clinical ground.

Large randomised trials have muddied the picture. A 2021 trial in the New England Journal of Medicine found live births in 77.2% of couples using PGT-A versus 81.8% using conventional IVF — no improvement for good-prognosis patients.

What none of these methods can do is reliably predict complex traits such as intelligence, personality or athleticism, which depend on interactions between thousands of genes and a lifetime of environment. That gap is where the marketing outruns the science.

The Problem With Polygenic Scores

Nucleus Embryo and similar services rest on polygenic scores: statistical summaries of the combined effect of thousands of genetic variants, each with a minuscule individual influence, on a given trait. At the population level these scores have real predictive value.

The catch is that population-level validity does not transfer cleanly to a single embryo. Four specific limitations make polygenic scores scientifically problematic for embryo selection, and each one narrows the promised benefit considerably.

The effect sizes are small

A polygenic score for educational attainment explains only about 12 to 16% of the variance in years of education, and cognitive scores capture less still. Within families, where embryo selection actually operates, the usable signal is roughly half that again.

Scores travel poorly across ancestries

Most large genetic studies were done in people of European descent, so the scores lose accuracy elsewhere. Research has found their predictive power falling by roughly two-and-a-half-fold in East Asian populations and nearly five-fold in those of African ancestry.

This is a serious equity problem baked into the method. One analysis of the first decade of polygenic-scoring studies found that around two-thirds used exclusively European-ancestry participants, meaning the tools work best for exactly the populations already best served by medicine.

Complex traits really are complex

Intelligence is not a simple sum of independent variants. It involves gene–gene interactions, gene–environment feedback and epigenetic effects that no current score captures — a theme explored in our piece on how the environment shapes gene expression.

A score predicts averages, not individuals

The embryo with the highest score is not guaranteed to become the child with the most of that trait. It is merely the one that, averaged across many similar embryos, would be expected to score slightly higher.

There is a subtler trap too. Siblings share much of their DNA, so the differences a score can act on within one family are far smaller than those it detects across a whole population. That is why real gains shrink below the headline correlations.

How Small the Real Gains Are

Peer-reviewed work has actually measured the likely benefit, and the figures are sobering. A 2019 study in the journal Cell by Ehud Karavani and colleagues modelled selecting the top-scoring embryo from a realistic IVF batch.

Their conclusion was that the average gain would be around 2.5 centimetres of height or roughly 2.5 IQ points. Crucially, they added that these averages come with wide prediction intervals, and that in large families the child with the highest score is usually not the tallest.

A 2021 analysis in the New England Journal of Medicine, led by Patrick Turley, reached the same broad verdict for education. Selecting the best of ten embryos yielded an expected gain of about 0.53 years of schooling for people of European ancestry, and less for other ancestries.

The uncertainty dwarfs the effect. The Turley team calculated that the actual outcome for a selected embryo could range from more than four extra years of education to more than three fewer. The chosen embryo might end up doing worse, not better.

That interval is the point too often lost in the sales pitch. A prediction can be perfectly valid across thousands of children yet nearly useless for the one child a couple is planning for. That gap is where the whole controversy lives.

For disease, the same paper found small but real absolute reductions when selection was done well: a few percentage points off the lifetime risk of conditions such as coronary artery disease and type 2 diabetes.

The authors stressed that such reductions should always be shown in absolute terms. A headline “relative” cut can sound impressive while the real change in a single child’s odds is a fraction of a percentage point, which is a very different thing to buy.

The Nucleus Embryo Claims, Assessed

The company behind the product was founded in New York in 2021 by Kian Sadeghi, then in his early twenties, and has raised tens of millions of dollars from prominent technology investors. At launch it did not biopsy embryos itself, but partnered with an existing clinical genetic-testing firm.

Parents would upload embryo data after standard clinical screening, then receive rankings across hundreds of conditions and dozens of additional analyses.

Nucleus Embryo marketed selection for resistance to heart disease and cancer, for intelligence and longevity, for body mass index, for eye and hair colour, and even for left-handedness and a predisposition to alcoholism. Each claim deserves its own scrutiny.

The Theranos Comparison and the Problem of Hype

The sharpest criticism of Nucleus Embryo is not that its technology is fake. It is that a genuine research tool has been repackaged into a consumer promise it cannot keep. That structural problem is what invites the Theranos comparison.

The parallel is imperfect. Nucleus uses real genomic technology, not fabricated results. But the shape of the risk rhymes: dramatic claims marketed to people willing to pay for control over something they care about, wrapped in science too complex for most buyers to check.

The stakes are unusually high because the customers are prospective parents and the product concerns their future children. A family may pay thousands, choose an embryo on a prediction that never materialises, then measure a real child against a number that was always shakier than it looked.

This is why the vocabulary matters. “Optimisation” implies a reliable dial the science does not provide. What the studies describe is a faint statistical nudge with an enormous margin of error — a very different thing from the confident language of a product page.

What the Ethical Debate Is Really About

The deepest concerns are not about the precise capabilities of one product. They are about direction of travel: the gradual normalisation of choosing children by predicted traits, and the social consequences that could follow.

The history of eugenics is the essential context. In the early twentieth century, scientific and political establishments across several countries embraced selective reproduction to improve populations. In the United States, sterilisation laws led to the forced sterilisation of tens of thousands of people.

In Nazi Germany the same logic escalated catastrophically. The 1933 sterilisation law was followed, according to the United States Holocaust Memorial Museum, by the forced sterilisation of around 400,000 people, and then by an organised murder programme.

Modern genomic selection differs in crucial ways. It acts on embryos rather than living people, it is voluntary, and its science is more sophisticated. But the underlying idea — that some genetic profiles are more desirable — echoes that history enough to demand caution.

Access and equity sharpen the concern. Effective embryo selection would first reach only affluent families who can afford IVF plus extra screening. Over time, a society where advantaged families select for health and cognition while others cannot would let genetic inequality compound economic inequality across generations.

The ancestry gap makes this worse. Because the underlying scores work best for people of European descent, any advantage the technology confers would flow unevenly, mapping onto existing lines of privilege rather than cutting across them. A tool sold as personal empowerment could deepen structural inequality.

There is a quieter worry too. Parents who pay thousands for a genetic ranking may come to view a child through that lens, measuring a living person against a prediction. How that shapes the parent–child bond is hard to foresee and harder to undo.

Where the Law Draws the Line

Regulation varies dramatically by country. In the United Kingdom the Human Fertilisation and Embryology Authority has been unambiguous: polygenic trait screening of embryos, known as PGT-P, does not fall within the purposes permitted by law and is therefore unlawful.

The regulator adds that there is no evidence supporting the clinical use of such screening to improve either the chance of a baby or that child’s later health. UK law also prohibits choosing an embryo’s sex for any reason other than avoiding a serious inherited illness.

The United States is far more permissive. Federal oversight of genetic tests is limited, resting mainly on laboratory quality standards and medical-device rules, with wide gaps for direct-to-consumer products, especially when a service presents itself as software rather than a diagnostic device.

That software framing is the crux. A product that merely presents information, rather than diagnosing or treating, can sidestep the stricter rules that would apply to a medical device — which is part of why a service unlawful in Britain can be sold openly in America.

Much of Europe sits closer to the UK. Germany, Spain, France, Italy and Norway restrict embryo selection to serious therapeutic purposes, which means a product like Nucleus Embryo cannot lawfully be offered in most of those countries.

The safe, regulated frontier of the field is better represented by advances covered in our report on gene editing in 2026.

For now the honest summary is narrow. Preimplantation testing to prevent serious single-gene disease is genuine, valuable medicine. Ranking embryos by predicted intelligence or longevity is not, and no amount of confident marketing changes what the peer-reviewed evidence actually shows.

What Scientists Say

Writing in Scientific American, bioethicists Arthur Caplan of New York University and James Tabery of the University of Utah drew a pointed comparison between Nucleus Embryo and Theranos, the blood-testing firm that vastly overstated its technology.

They were careful to note there is no sign of the deliberate deception that defined Theranos. The parallel was structural — a real underlying technology stretched into claims that entice investors and wealthy customers but do not survive scrutiny.

“The real danger is that a bunch of wealthy parents-to-be who are too eager to control their children’s biological future will shell out $5,999 for a product that offers no such control.”
— Arthur Caplan & James Tabery, bioethicists. Scientific American, 2025.

Reproductive-medicine specialists have echoed the caution. The researchers behind the Cell and New England Journal of Medicine analyses above consistently find that predicting complex traits from embryo DNA delivers far less than the marketing implies. Nucleus and its founder have called the Theranos comparison unfair.

Frequently Asked Questions

Sources

Primary peer-reviewed research:

1. Karavani, E., et al. (2019). Screening Human Embryos for Polygenic Traits Has Limited Utility. Cell, 179(6), 1424–1435. doi.org/10.1016/j.cell.2019.10.033
2. Turley, P., et al. (2021). Problems with Using Polygenic Scores to Select Embryos. New England Journal of Medicine, 385(1), 78–86. doi.org/10.1056/NEJMsr2105065
3. Okbay, A., et al. (2022). Polygenic prediction of educational attainment within and between families. Nature Genetics, 54(4), 437–449. doi.org/10.1038/s41588-022-01016-z
4. Martin, A. R., et al. (2019). Clinical use of current polygenic risk scores may exacerbate health disparities. Nature Genetics, 51(4), 584–591. doi.org/10.1038/s41588-019-0379-x
5. Herskind, A. M., et al. (1996). The heritability of human longevity: a study of 2872 Danish twin pairs. Human Genetics, 97(3), 319–323. doi.org/10.1007/BF02185763

Institutional / science journalism:

6. American Society for Reproductive Medicine (2024). The use of preimplantation genetic testing for aneuploidy: a committee opinion. Fertility and Sterility. asrm.org
7. Human Fertilisation and Embryology Authority. PGT-P is not lawful in the UK. hfea.gov.uk
8. United States Holocaust Memorial Museum, Holocaust Encyclopedia. Eugenics. encyclopedia.ushmm.org
9. Caplan, A. & Tabery, J. (2025). The Myth of the Designer Baby. Scientific American. scientificamerican.com