Assisted reproduction has advanced at a dizzying pace in recent years and, with it, new questions have emerged—questions we couldn’t even imagine before. One of the most common is whether it’s possible to choose physical traits such as eye color or even the baby’s sex. Spanish legislation is very clear on this matter: selecting these characteristics is not allowed, except in very specific situations related to health.
The Spanish Law 14/2006 on Assisted Human Reproduction Techniques establishes that embryo diagnosis or selection must always have a therapeutic purpose. In other words, embryos can only be acted upon to prevent serious diseases or to conduct genetic studies with a defined clinical objective. Therefore, choosing specific traits, as if designing “babies to order,” is completely outside the Spanish legal framework.

It is common for patients to ask whether they can choose the sex of their future baby, but Spanish law is strict: sex selection is permitted only when there is a real risk of transmitting an X-linked disease that could seriously compromise the child’s health. Outside this context, choosing the sex is strictly prohibited.
A similar situation occurs with eye color. Even without an explicit legal prohibition, the reality is that this trait is far too complex for precise selection. Eye color is influenced by multiple genes, genetic interactions that are not yet fully understood, and variations that cannot be accurately predicted. In this case, the limitation is not only legal but also scientific.
Spain maintains one of the most advanced—and at the same time strictest—regulations in the world regarding assisted reproduction. The techniques allowed in the country help prevent hereditary diseases, improve pregnancy rates, and support individuals and couples who otherwise could not have children. However, this progress is supported by the fundamental principle that technology should be used to protect health, not to design non-medical characteristics.

In essence, the law seeks to establish an ethical boundary that preserves the original purpose of assisted reproduction against the temptation of imagining a future where everything can be chosen. Reproductive medicine, after all, was not created to shape personal preferences but to treat fertility issues and prevent serious diseases.