In late November, Emma Wren Gibson was born just in time for the Christmas season—and 25 years after her conception.

A quarter century ago, fertility doctors froze Emma while she was still an embryo created during the process of in vitro fertilization (IVF). Many parents who bear children through IVF choose to freeze indefinitely any remaining embryos after they have the number of children they desire (or if the mother can’t carry more unborn children).

At least 600,000 embryos sit frozen in storage facilities across the United States, according to the Department of Health and Human Services. Some reproductive experts believe the number is closer to 1 million.

Among those frozen long-term, a small fraction of little ones get a chance to live, when couples like Tina and Benjamin Gibson adopt embryos like Emma. Early last year, a physician at the National Embryo Donation Center—a Christian organization based in Knoxville, Tenn.—transferred embryo Emma into Tina’s womb.

On Nov. 25, 2017, baby Emma arrived healthy and whole, weighing 6 pounds, 8 ounces. She likely holds the record for the embryo longest-frozen before birth. Tina, 26, marvels at the process, noting she was a 1-year-old baby when physicians created her daughter in a lab dish.

“People say, ‘Oh, it’s science,’ but … I think it’s a gift from the Lord,” the new mother told a local news station in December. “It’s a gift from the Lord, for sure.”

Not all fertility doctors view it this way. For many physicians, creating embryos and successfully transferring them into their mothers’ wombs—or the womb of an adoptive mother—is a mixture of science and odds. And the so-called “odds” for embryos often aren’t good.

Some embryos don’t successfully implant in the womb. Others don’t survive the thawing process. And many don’t survive the initial screening process to determine whether they should have a chance at life at all. If a pre-implantation test indicates a potential chromosomal abnormality, physicians often discard or freeze the embryo and move on to stronger prospects.

But one problem with the screening process is that it isn’t always accurate.

Over the last few years, a handful of physicians in the United States and Europe have reported that embryos deemed abnormal by early tests could still grow into normal pregnancies—and they have the healthy babies to prove it.

That means physicians have thrown away perhaps tens of thousands of embryos deemed abnormal that could have been healthy. Norbert Gleicher, a New York fertility physician involved in the research, has called it “an unprecedented scandal.”

“We as a profession have been disposing of thousands and thousands of completely normal embryos, with normal potential,” Gleicher told New York magazine last year. “And nobody—nobody—has had the guts to stand up and say we are sorry.”

Gene Rudd, a physician and senior vice president of the Christian Medical & Dental Associations, sees an even bigger scandal: a preoccupation with testing embryos in fertility clinics and babies in wombs to choose those deemed most desirable.

Rudd calls it a “cultural bent on search and destroy. … This notion that life is disposable if we don’t get exactly what we want.”

As physicians debate the accuracy of tests for embryos in test tubes and babies in the womb, others are bent on search and rescue: adopting embryos out of frozen storage and advocating for children and adults who have shown that a life with disabilities is a life worth living too.

MONICA HALEM KNOWS FIRSTHAND the anguish of nearly discarding her child. The New York dermatologist and single mother bore her first daughter in 2013 through IVF. Nearly two years later, at age 44, she began IVF again, but physicians told her that testing showed all her embryos were abnormal.

When pre-implantation genetic screening (PGS) shows a chromosomal abnormality that could make an embryo unlikely to live to birth—or could result in a condition like Down syndrome—physicians often advise discarding those embryos and trying for presumably healthier ones.

But some physicians weren’t convinced the PGS testing always produced accurate results.

Jeffrey Braverman, a New York fertility doctor, had grown suspicious of test results when he saw a handful of younger patients producing abnormal embryos. He joined a program to implant presumably abnormal embryos into older women. Eight women agreed. Five became pregnant. All five women delivered healthy babies.

Braverman encouraged Halem to try a similar approach. In such a scenario, a woman might still abort a baby if later tests showed the unborn child did have abnormalities. This wasn’t a pro-life program, but it yielded live results: In January 2016, Halem delivered another healthy baby girl.

Meanwhile, Norbert Gleicher was alerting his colleagues to the alarming findings. In October 2015, he told the American Society for Reproductive Medicine (ASRM) that in some cases abnormal embryos had been born normal infants.