A fetus lives in a world of bubbles. In its earliest days, it’s shaped like one. Later, it floats in one—the squishy, enveloping amniotic sac. And eventually, if all goes well, the fetus releases one bubble of fluid, then another and another, like smoke signals, as it puckers and swallows and floats in the womb.

It was the bubbles that first convinced Hung-Ching Liu two years ago that a baby might actually be grown outside its mother’s uterus. Liu, the director of the Reproductive Endocrine Laboratory at Cornell University’s Center for Reproductive Medicine and Infertility in Manhattan, has become, almost accidentally, the nation’s premier womb-maker. Beginning in 2001, her lab started growing sheets of human tissue composed of cells from the endometrium, the lining of the uterus. This engineered tissue, which used starter cells donated by infertile patients, was meant to bolster the clinic’s in-vitro fertilization success. A layer of endometrial cells is, after all, the ideal platform on which to nurture an embryo, a medium almost as good as mom would have made.

But the tissue, a single layer of cells stretched across a cell culture within a plastic petri dish, was gossamer-thin. “We’d hoped the embryos would implant on this tissue,” Liu says, “so we could learn more about the mechanisms of implantation. But they could not.” The growing embryos would break through the tissue, smack against the petri dish and, like a tree whose roots hit rock, die.

So Liu added layers, tissue atop tissue, until she had a three-dimensional model, essentially a freestanding uterus. Embryos could attach to this engineered tissue. They could burrow in, sending out shoots of blood vessel. They could take in nutrition and give out waste. They could divide, differentiate, and thrive.

Which led at last to the bubbles. In 2003, in an experiment that hasn’t received as much attention as one might expect—perhaps because Liu hasn’t published her results, due to her qualms about how those results will be received by politicians, activists and desperate would-be parents—a mouse embryo grew almost to full term in one of Liu’s artificial wombs. It moved. It breathed. It bubbled. “And not just one bubble,” Liu says. “We saw bubble, bubble, bubble.”

She may also have glimpsed, in that moment, the far-out future of human reproduction, vitreous and shifting. Thanks to her research and others’, man-made mouse wombs could be a reality within a decade—and a stepping stone to artificial human wombs. Eventually, these baby incubators could supplant natural ones. Conception could be clinical, and birth bloodless. Gestation could be detached from motherhood, and a fetus could be viable from the instant that sperm and egg fused.

Or not. Days after cheerfully percolating, Liu’s rodent fetus died, deformed and contorted, more seahorse than mouse, a developmental freak. The same thing happened to the next fetus she implanted, and the one after that. “Making babies is more complicated than we imagined,” Liu says. “And we knew going into this that making babies is very, very complicated.”

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