More than 1,000 couples were surveyed for the study led by Anne Lyerly of Duke University, USA Today reported. More than half said that they were unlikely to donate embryos they did not need to another couple.

That finding was surprising, given the terms of the debate on in vitro fertilization and the fate of embryos couples do not need, Lyerly said.

"If you look at the policy debate and the discussion in the literature, there is a presumption that if you respect or care about an embryo, you would want it to become a child," Lyerly said.

Forty percent of the couples who said they did not want more children said they would prefer to donate surplus embryos for research, as did 15 percent who were considering more children. But the federal ban on funding for research on embryos means many clinics do not offer that choice.

Many couples simply leave the embryos in storage, paying fees indefinitely, Lyerly said. She said couples appear to feel responsible for those embryos to the point of not wanting to let them go to unknown parents.