Scientists have created the first-ever fully grown human eggs. Although more work is needed, the breakthrough finding has the potential to improve fertility treatments.

Normally, a woman’s eggs mature inside her ovaries once she’s hit puberty. Researchers at the University of Edinburgh and the Center for Human Reproduction in New York wanted to try to grow eggs outside the body. They accomplished this feat; however, the eggs have yet to be fertilized.

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“It’s very exciting to obtain proof of principle that it’s possible to reach this stage in human tissue,” Evelyn Telfer, a biology professor at the University of Edinburgh who helped develop the eggs, told the BBC.

Eggs have previously been grown in mice tissue that was removed from their bodies. Figuring out how to allow the eggs to fully mature in such a way for humans has proved to be much more difficult, partially because our tissue is more complicated than mouse tissue, Telfer explained to the New Scientist.

Telfer, who worked alongside scientists from the Center for Human Reproduction in New York, grew the eggs using samples collected from 10 women who chose to undergo caesarian sections. From those samples, they collected 310 “primordial follicles,” a tightly packed structure that has the ability to produce an egg cell. Among those follicles, 87 survived the initial growth stage and were able to be dissected for further culture, according to the findings published January 30th in the journal Molecular Human Reproduction.

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Out of those 87 samples, nine developed fully.

“We had no great expectations. To see at least one [egg reaching maturity], we thought, ‘Wow, that’s actually quite incredible,’” Telfer told Science

The next step is to fertilize the eggs, which would then reveal how viable they truly are. However, the team hasn’t yet received regulatory approval for fertilization, Telfer explained in a statement. Right now, the process would be illegal without receiving a license from the United Kingdom's Human Fertilization and Embryology Authority.

If one day they’re able to fertilize the eggs and they prove to be healthy, this could change the lives of girls with cancer by protecting their fertility. And even if that never happens, the research has still allowed them to better understand how human eggs develop.