Scientists have turned skin cells into fully functional eggs that led to eight mouse babies being born. It’s a promising procedure that one day could help humans with fertility issues.

The team of Japanese researchers led by Katsuhiko Hayashi first took cells from the tails of 10-week-old female brown mice. (That’s about 30 in human years.) Next, they turned the skin cells into a special type of cell called induced pluripotent stem cells, which can divide and form different cells, according to the study published this week in Nature Research.

Unfortunately, two of the mouse babies were eaten by their mothers

The pluripotent stem cells were covered with chemicals that encouraged them to specifically turn into immature egg cells. After adding some tissue from the ovaries of mouse fetuses, they became mature eggs. Finally, the researchers fertilized the eggs and transplanted the embryos into surrogate mice. In total, eight mouse babies were born from 1,348 embryos.

This is an exciting step forward, but there are several big limitations. One is that the process didn’t work most of the time and even when it did, the eggs weren’t very healthy. After all, only eight mouse babies were born from over a thousand embryos. Of those, two were eaten by the mothers, possibly because they were abnormal.

The hope is that eventually this same technology could be applied to humans whose eggs aren’t fertile — but this will take years. We are so much more complicated than mice, and there are many ethical issues. But now, we know that this sort of procedure is at least possible.

"If we could make human eggs, it could be a very powerful tool for curing infertility, Hayashi told New Scientist about the technique. "From a technical point of view it could work."