What is an embryo?

It sounds like a simple question. You could look it up in a dictionary. But when you start unpacking it – what embryos are, what they're not, what they might become – it all gets complicated fast.

Add scientific advances in reproductive technology, different and sometimes inconsistent definitions, and evolving legal and ethical frameworks, and the complexity multiplies. Simple questions rarely have simple answers.

That's why, in January 2026, a one-day workshop brought together scientists, lawyers, ethicists, and policy experts from the UK, Sweden, Germany, and beyond. Held at the Wellcome Collection in London, "Embryos and liminal entities: Rethinking questions of status and protection in shifting scientific, legal and ethical landscapes" focused on two questions:

1. What is an embryo?
2. Do all embryos and embryo models merit the same protections in law?

The aim wasn't to reach consensus; it was to develop a shared understanding of the landscape, identify pressure points, and recognise where regulation and policy change might be needed.

This was a University of Sheffield ESRC Impact Acceleration Account (IAA) funded event in collaboration with the Future of Human Reproduction, organised by Professor Sara Fovargue and Dr Laura O’Donovan from the School of Law at Sheffield who are members of the FoHR team.

Science panel

The morning began with scientists sharing their working definitions. One speaker described an embryo as "a self-organising living system" and "a transient structure during pregnancy." An embryo:

• Originates from a fertilised egg
• Undergoes early cell divisions following fertilisation
• Relies on supporting tissues like the placenta for development
• Lays the foundation for a newborn
• 
  

Crucially, an embryo has developmental potential: the capacity to become to a viable fetus.

A second speaker then explained what embryo models are – and critically, what they're not. Embryo models are created from stem cells and aim to replicate the human embryo at different stages of development, they can help scientists study how tissues and organs begin to form, why some pregnancies fail, and how congenital conditions arise. They can also be used to test treatments or drugs without using natural embryos. They differ from embryos in several ways:

• They don't originate from fertilised eggs – they're created from stem cells
• They don't undergo those early cell divisions in the same way
• While they can self-organise to some extent, this doesn't fully mirror embryo development and is far more variable
• Their quality largely depends on their starting materials

The key difference is that embryos can develop into babies. Embryo models currently cannot.

This distinction matters for how we think about regulation. Should only embryo models that develop the capacity to become a viable fetus have the same legal status as embryos, as a member of the panel suggests?

But then the conversation got (more) complicated.

A third speaker introduced in vitro gametogenesis (IVG), which could create eggs or sperm from other cell types like skin cells, rather than from reproductive organs. This could help cancer survivors with lost reproductive function, those with developmental infertility, and same-sex couples. It could also enable same-sex couples to both be genetically related to their offspring and allow transgender individuals and post-menopausal women new reproductive possibilities.

This complicates the question, “what is an embryo?” because, with IVG, the embryo comes from eggs and/or sperm that came from (e.g.) skin cells, rather than from a person’s reproductive organs. So, if embryos are defined in terms of having originated from fertilisation, what does it mean when those eggs or sperm were created from skin cells? Does how and where the egg was created make a difference to whether it is an embryo, or to what type of embryo it is?

The panel also raised concerns about one potential application of IVG: "solo reproduction" – one person creating a child using both egg and sperm created from their own stem cells. The genetic risks would be significant. We all carry several harmful genetic variants that don't usually affect us because we have two copies of each gene. Solo reproduction would dramatically increase the probability of a child inheriting two copies of the same harmful variant.

This raises another question: if embryos are defined by their potential to develop, how should we think about embryos with different likelihoods of healthy development?

Law panel

The session began with the introduction of the Human Fertilisation and Embryology Act 1990 definition: "embryo means a live human embryo where fertilisation is complete".

Under the Act, you need a licence to create human embryos outside the body. Some activities can't be licensed – including replacing the nucleus of an embryo with a nucleus from another person or embryo.

This definition was challenged in 1997 with the creation of Dolly the sheep through cloning (somatic cell nuclear transfer (SCNT)). Scientists took a nucleus from one cell and put it into an egg cell. The process didn't involve fertilisation. So the question at the time was - is this covered by existing law or not?

The courts ruled that cloned embryos do count as embryos in law because they function the same way and have the same ability to develop into a human being. The key legal issue was function and developmental potential, not the method of creation.

The 1990 Act was amended in 2008, but questions remain.

A parallel was drawn with neural organoids – small, lab-grown three-dimensional structures that are made from stem cells to model different aspects of the developing brain. Both neural organoids and embryo models are becoming more complex and raise parallel questions about oversight. For neural organoids, a key question is about capacity for pain or awareness. For embryo models, it's more about developmental potential. But both highlight the same issue: regulatory gaps.

Questions of consent were also raised: Do people understand what can be created from their donated cell lines? Should there be opportunities for re-consent when significantly novel uses emerge?

The panel also explored how patent law approaches embryos. European patent law focuses on an embryo's capacity to become a viable fetus. But patent law alone, they argued, is poorly equipped to address broader social concerns about access to medicine or the morality of commercial exploitation.

Ethics panel

There is widespread disagreement about the moral status of embryos, founded on different fundamental views. Questions about when something possesses a soul, has potential, has value, or develops cognitive capacity are highly debated.

The panel asked whether IVG changes how we should think about moral status:

• Does it matter that IVG makes it easier to generate large numbers of embryos?
• Does it matter that IVG embryos might be less likely to lead to a live birth?
• Does it matter that IVG embryos might be less emotionally tied to existing people, less socially embedded?

A thought experiment was posed: "If I destroy an embryo's structure but keep the cells alive in a condition that would allow me to reassemble the embryo later with the same genetic properties, would that mean I had retained the embryo's potential to become a person? If, if it does, was its destruction not (or less) morally problematic?"

This question highlights a key issue about how we think about what counts as having potential.

The panel noted that how we think about embryos is unstable and that current regulation is a compromise. If potential matters, it's about intrinsic capacity – you either have it or you don't. The problem with embryo models is that we cannot fully know their potential until they are created and tested.

A provocation was also offered: that we might be focusing on technical definitions as a way of avoiding some hard ethical questions.

Current country legal and ethical protections

The afternoon session looked at how different countries approach these questions.

Sweden's framework uses the phrase 'fertilised eggs' rather than 'embryos', and the key analytical question centres on what properties give embryos special status, and whether embryo models can share these properties.

Under Germany's current regulatory framework, embryo use is permitted only for reproductive purposes. Two separate pieces of legislation define "embryo" differently, a tension that has contributed to people seeking treatment abroad and concerns about the country's ability to retain scientific talent. Proposals to ease these restrictions remain unimplemented

From a European Court of Human Rights perspective, whilst there is consensus on the need for protection of embryos in vitro, significant debate continues regarding what defines an embryo, its status, and what form protection should take. Ambiguity in legal frameworks presents challenges for establishing clear protections; courts will need to develop interpretative boundaries as part of their role in applying human rights law.

Approaches to regulation

For the final sessions of the afternoon, the conversation turned to how we might actually govern these technologies.

A case was made for principles-based regulation rather than rigid rules – focusing on communal goals, facilitating stakeholder collaboration, ensuring regulation is knowledge-based and responsive. The benefits: flexibility, future-proofing, supporting innovation whilst maintaining consistency.

It was also suggested that, at least initially, a Code of Practice for embryo models could offer a practical solution. It would create clear rules and build public confidence without needing to change the law. The approach moves away from blanket limits like the 14-day rule towards assessing each research project individually. Three key elements would be involved: expert oversight for all research, flexible limits tailored to each project's purpose (with clear end points), and firm red lines (such as no ectogenesis, and no human reproductive use).

The need for bespoke regulation of embryo models was also discussed – that regulation would better fit the technology, encourage investment, and support responsible innovation. The recommendation emerging from this discussion was to maintain the distinction between embryos and embryo models whilst getting relevant regulators ready, using the time ahead for learning.

The need to move away from binary yes/no decisions towards dynamic and conditional approaches was highlighted – starting earlier with applicants, setting conditions of use, and requiring follow-up. But this raised further questions: how receptive are regulators to collaborative working? And what happens when large-scale commercial actors enter the space?

Summary and next steps

The workshop explored two questions: What is an embryo? And do all embryos and embryo models merit the same protections in law?

Scientifically, embryos come from fertilised eggs and can develop into babies. Embryo models are created from stem cells and currently cannot. But emerging technologies like in vitro gametogenesis (IVG), which could create eggs or sperm from skin cells, complicate this distinction.

Technologies can develop faster than ethical or legal definitions and we cannot fully know an embryo model's potential until it has been created and tested, meaning we sometimes need to regulate based on anticipation rather than hard evidence.

Several regulatory approaches were proposed – principles-based regulation, codes of practice, bespoke frameworks, and dynamic conditional approaches. Each offers different ways to balance protection with innovation.

Key questions remain: What properties give embryos their special status? When does complexity require regulatory intervention? What role should the public play in these decisions?

These questions don't have simple answers. But asking them together – scientists, lawyers, ethicists, policymakers, and in the future, the public – is how we begin to work out what matters and why. An outcome of this workshop will be a discussion paper or note that captures these conversations – not as conclusions, but as waypoints in an ongoing dialogue. Watch this space.

This event was held under Chatham House rule. Views and contributions are not attributed to individual speakers or their organisations.

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