The precursors to human eggs have been grown to full maturity outside the body for the first time.

The news: By carefully controlling conditions like oxygen levels and nutrients, as well as variables such as the surfaces on which precursor cells are grown, researchers from the University of Edinburgh in the UK coaxed these cells into fully developed eggs in 22 days. Usually it takes five months in the body.

Why it matters:  As the BBC notes, it could enable young female cancer sufferers who are made infertile by chemotherapy to later use their own eggs during IVF. It also gives researchers a rare chance to study how eggs develop.

But: While the eggs reached maturity, it’s unclear if they’re healthy, or whether they can be properly fertilized into an embryo. Those experiments are next on the researchers’ to-do list, though such tests will need approval and, for ethical reasons, will study only the very first stages of development.