Scientists have created human eggs in the lab using a similar process to the one used to clone the famous Dolly the sheep, then used in vitro fertilization (IVF) to turn them into embryos.

Although this method is far from being used in a clinical setting, the hope is that it could eventually pave the way to new fertility treatments.

“In addition to offering hope for millions of people with infertility due to lack of eggs or sperm, this method would allow for the possibility of same-sex couples to have a child genetically related to both partners,” study co-author Dr. Paula Amato, a professor of obstetrics and gynecology in the Oregon Health & Science University (OHSU) School of Medicine, said in a statement.

The proof-of-concept experiment was described in the journal Nature Communications. The egg-making process involved removing the nucleus from an existing human egg cell and swapping it out for a nucleus from a human skin cell. This first step, called somatic cell nuclear transfer, has been used to clone a variety of animals, including Dolly.

But the OHSU researchers aimed to make a functional egg, not a clone, and eggs carry half the chromosomes as nonreproductive cells in the body do. During fertilization, an egg’s 23 chromosomes combine with 23 chromosomes from a sperm cell, resulting in a total of 46. To prompt their makeshift eggs to shed half their chromosomes, the scientists applied an electrical pulse and a drug called roscovitine, which messes with enzymes that regulate the cell cycle, the process by which cells divide.

This experiment ultimately resulted in 82 egg cells that were then fertilized with sperm via in vitro fertilization (IVF), according to the statement. However, the fertilization step isn’t yet foolproof — only around 9% made it to the “blastocyst” stage. At that point, the egg has divided to form a hollow sphere of cells that could be introduced to the womb via IVF.

Most of the eggs fertilized in the study didn’t make it to the blastocyst stage, and in fact, only divided enough times to produce four to eight cells overall. The “modest” blastocyst development rate likely stems from two factors, the study authors wrote in their paper. For starters, chromosomal abnormalities likely stopped the fertilized eggs from dividing further. And second, the genes swapped in from skin cells likely weren’t successfully reprogrammed to sustain embryonic development. In other words, in some ways, the genes were still activating as if they were in skin cells, not the cells that form early in development.