Nearly 40 years after the world was jolted by the birth of the first test-tube baby, a new revolution in reproductive technology is on the horizon — and it promises to be far more controversial than in vitro fertilization ever was.

Within a decade or two, researchers say, scientists will likely be able to create a baby from human skin cells that have been coaxed to grow into eggs and sperm and then used to create embryos that can be implanted in a womb.

The process, called in vitro gametogenesis, or IVG, so far has been used only in mice. But stem cell biologists say it is only a matter of time before the procedure could be used in human reproduction.

With IVG, two men could have a baby that was biologically related to both of them, by using skin cells from one to make an egg that would be fertilized by sperm from the other. Women with fertility problems could have eggs made from their skin cells.

“It gives me an unsettled feeling because we don’t know what this could lead to,” said Paul Knoepfler, a stem cell researcher at the University of California, Davis. “You can imagine one man providing both the eggs and the sperm, almost like cloning himself. You can imagine that eggs becoming so easily available would lead to designer babies.”

Some scientists are even talking about what they call the “Brad Pitt scenario” when someone retrieves a celebrity’s skin cells from a hotel bed or bathtub. Or a baby might have what one law professor called “multiplex” parents.

“There are groups out there that want to reproduce among themselves,” said Sonia Suter of George Washington University. “You could have two pairs who would each create an embryo, and then take an egg from one embryo and sperm from the other, and create a baby with four parents.”

Still, how soon IVG might become a reality in human reproduction is open to debate.

“I wouldn’t be surprised if it was 5 years, and I wouldn’t be surprised if it was 25 years,” said Jeanne Loring, a researcher at the Scripps Research Institute.