The nation's 500,000 frozen embryos face a hotly debated future.

Researchers want them to help cure debilitating diseases, parents wonder whether they should be stored or destroyed, and still others see them as a way for infertile couples to adopt and become pregnant at the same time.

The last path is a little-known but growing option at the heart of a Monday ruling that bars federal funding of embryonic stem-cell research. The Obama administration is expected to appeal the order, which was sought by Nightlight Christian Adoptions and others who oppose research that destroys embryos.

Nightlight and a handful of similar agencies - including Cincinnati-based Embryos Alive - match prospective parents with cryogenically frozen embryos left over from in-vitro fertilization procedures.

Websites list dozens of available embryos, along with lab reports and short bios of the sperm dads and egg moms.

"Potential adopters call every day," said Bonnie Bernard, who founded Embryos Alive seven years ago and reported its first successful birth in 2004.

The Cincinnati agency used to complete an embryo adoption once every three months. Now, a match is made every two weeks, "and about once a month we're either getting positive or negative news" about an attempted pregnancy, Bernard said.

Nightlight started the Snowflakes Embryo Adoption & Donation Program, the nation's first, in 1997.

"This summer, we just celebrated the birth of our 235th child," said Kimberly Tyson, manager of Nightlight's embryo-adoption-awareness center in Loveland, Colo. "Embryos that have been frozen 12 years have produced healthy children."

But despite the rising number of couples willing to try, embryo adoption is still a long-shot chance at pregnancy.

"The national average is that about 40 percent survive the thaw," Bernard said. "And after that, there's about a 50 percent chance that they'll stick."

The number of frozen embryos made available for adoption also is comparatively small - not much more than 2 percent of the thousands kept in storage, Bernard said.

She thinks part of the reason is that parents who donate leftover embryos must go through the same screening as paid donors, a process that many decide against.

The rising surplus of frozen embryos results from the popularity of assisted reproductive procedures such as in-vitro, in which multiple eggs are harvested and fertilized for transfer to a woman's womb. Oftentimes, many embryos are left over, and parents must decide whether to donate, destroy or store them indefinitely.

"Clinics have been anonymously donating embryos to people for a long time - probably long before Snowflakes started," Tyson said. Among the eight agencies or centers nationwide that have a stated embryo-adoption program, an estimated 3,000 children have been born since the late 1990s, she said.

Only one state, Georgia, has a specific embryo-adoption law.

Bernard thinks there could be room for compromise on the stem-cell issue - that non-viable, or fragmented, embryos could be approved for research while others are kept.

"It's mostly black and white," she said of the debate. "But maybe there is some gray."

Tyson said Nightlight's pro-life stand isn't likely to change. She said she knows of one embryo that was frozen, thawed, re-frozen and thawed again.

Now, Tyson said, "He's a sweet little 3-year-old boy."

rprice@dispatch.com