In the beginning, embryos created through IVF were implanted in the womb right away. The first IVF baby, Louise Brown, was born in 1978. It took six more years before doctors perfected the freezing and unfreezing technique. Zoe Leyland, the first baby from an embryo frozen after IVF, was born in Australia in 1984. The embryo had been frozen for what we might now consider a brief two months. Doctors in the United States, Britain, Israel, the Netherlands, and West Germany quickly picked up the procedure; over the next two years, more than two dozen babies were born from frozen embryos.
The ability to stop time, even briefly, offered practical advantages. Before cryopreservation, embryos had to be implanted all at once or discarded; now extra embryos could be saved for later, reducing the chance of twins and triplets. Doctors could wait for the moment a mother’s body was most ready to accept an embryo. And it eventually became possible, as predicted, to use the extra time to test embryos for genetic disease. (Actual designer babies are still far from reality, though.)
Freezing also bought time for families who were uneasy about discarding their extra embryos, but who were not sure about donation, either. Today, as many as a million frozen embryos are stored in tanks of liquid nitrogen. They remain even when their genetic parents die or divorce, inevitably raising legal questions. There are ethical questions, too: The National Embryo Donation Center, where the Gibsons “adopted” Emma, is a Christian fertility center whose purpose includes “protect[ing] the lives and dignity of frozen embryos.”
To make it even more complicated, no one knows exactly how long frozen embryos can remain suspended in time. The only way to know is to keep waiting. There are no official records on how long eggs are frozen before being implanted, but before Emma, the oldest known embryo that resulted in a live birth had been frozen for 20 years. A woman in New York gave birth to the boy in 2010. And in 2013, a woman gave birth from a 19-year-old embryo.
Theoretically, the reproductive specialist Barry Behr once told Scientific American, frozen embryos might last as long as a century or two. The real hitch, he said, is how cryopreservation could scramble ideas of family and generations:
The nature of reproduction and building families does not really foster an environment that would allow you to wait 50 years before you thaw your embryos out. Unless your daughter wanted to carry her sibling, for example, which in theory is possible: A person born from IVF may still have sibling embryos frozen and when they reach 30 and are infertile could technically thaw out the embryos that were created at the same time they were created, gestate them, and deliver their sibling. That hasn’t happened yet but it could be possible.
There may another practical consideration, too. Embryo-freezing technology has changed considerably in the last 25 years, and different freezing techniques require different thawing techniques. Deborah Wachs, a doctor at the Reproductive Science Center of the Bay Area, where the 19-year-old embryo was thawed and implanted, says that her center was transitioning from an older slow-freezing technique to a new vitrification technique at the time. Their longtime lab director had been there since the embryo was first frozen.
“If you look at a new embryologist coming out, they will likely never slow freeze in their entire careers because all they will know is vitrification,” Wachs says. In 10 years, she notes, everyone will be much less familiar with how to thaw slow-frozen embryos. The limiting factor on how long frozen embryos can remain suspended in time may not be physics or biology, but the half-life of human knowledge.