As evangelical Christians, Paul and Susan Lim believe that life begins at conception. So when they decided to have a third child, in vitro fertilization was out of the question, since the process often yields extra embryos.

But “adopting” the frozen embryos of another couple who had gone through I.V.F. was not.

Dr. Lim called it a “rescue operation.” To him, transferring donated embryos to his wife’s uterus was akin to saving a life. “These children are being abandoned in a frozen state,” he said. “If they don’t get adopted, they’re dead.”

As I.V.F. becomes more widespread and the number of spare embryos rises, giving birth with donated embryos is becoming more popular, especially among couples who oppose abortion and are struggling with infertility. But many of the agencies that offer donated embryos, including a vast majority of those supported by federal grants, are affiliated with anti-abortion rights or Christian organizations, leading some people to question whether single people, gay couples and others who might be interested could be missing out.

Even the term “embryo adoption” is caught up in the rhetoric of debate over abortion.

“The issue in the medical community is that by calling it ‘adoption,’ we give too much personhood to the embryo,” said Kimberly Tyson, the marketing and program director at Snowflakes Embryo Adoption in Loveland, Colo.