Debate about the use of leftover frozen embryos in stem-cell research might stir opposition among abortion opponents to in vitro fertilization, the process for which those embryos are made.

Congress is unlikely to restrict fertility clinics, but supporters of stem-cell research may inadvertently have reignited decades-old questions among religious conservatives about whether the end justifies the means if enabling childless couples to start families requires creating embryos that get used in medical research or are destroyed.

Supporters of increased research into embryonic stem cells cite the existence of 400,000 frozen embryos in clinics — many of which may ultimately be discarded as a reason for permitting more study of possible medical uses for stem cells.

“The whole issue of how many embryos are being created is a major source of debate,” commented Elizabeth Wenk, spokeswoman for Rep. Mike Castle (R-Del.), the lead sponsor of a bill to ease limits on funding embryonic-stem-cell study that passed the House in May.

Many lawmakers opposed to abortion have joined the cause of embryonic-stem-cell research, such as Sen. Orrin Hatch (R-Utah), but others are unconvinced by the surplus-embryos argument.

In vitro fertilization has become increasingly popular since the first test-tube baby was conceived in 1983. According to a 2002 report by the Centers for Disease Control and Prevention (CDC), the use of in vitro fertilization has “increased substantially” and is approaching 1 percent of all live births in the United States.

“There would be a huge uproar” if the federal government moved to restrict the activities of fertility clinics, said a Republican operative working to pass legislation to expand embryonic-stem-cell research.

One lawmaker already has questioned whether fertility clinics need to be subjected to more controls. In May, Sen. Sam Brownback (R-Kan.) suggested on ABC News’ “This Week” that limits to the number of embryos might be proper.

Carrie Gordon Earll, senior analyst for bioethics with Focus on the Family, said the stem-cell-research debate has cast light on the fate of surplus embryos. “People were shocked” to learn how many frozen embryos were in storage that likely would never be implanted in the mother.

American Society for Reproductive Medicine (ASRM) spokesman Sean Tipton agreed that talk about stem cells could bring negative attention to in vitro fertilization in the short term. He predicted that public support would not waver, however. “I don’t think Congress is ever likely to pass anything” to hamper fertility treatments, he said.

Fertility doctors should concentrate on “maximizing the chances of a successful treatment,” Tipton said, rather than setting limits on the number of embryos they create. Wenk suggested that legislating in this area would be difficult. “I don’t know if it can be dictated by Congress;

The number of embryos with uncertain futures is “an issue that comes up when you look at the big picture” of stem-cell research, human cloning and abortion, Earll insisted.

“It is an industry, and it is unregulated,” Earll said. “Is this industry going to police itself?”

Fertility clinics vary in how they advise their patients about the eventual fate of the embryos they create. Establishing a uniform code of “informed consent” for patients should be the first step, whether by the clinics or the government, Earll said.

“I guess it depends on the doctors,” Wenk allowed, while noting that Castle’s bill would create a mechanism for ensuring patients were fully informed.  The ASRM has long offered guidelines for informed consent, Tipton said.

Some proponents of abortion-rights and increased embryonic-stem-cell research decry the conservatives’ arguments as Trojan horses attempting to disguise a more sweeping goal: curbing access to fertility treatments.

“Severely limiting or banning [in vitro fertilization] is the true agenda of some opponents of stem-cell research. People need to realize that,” said Joshua Freed, chief of staff for the lead Democratic sponsor of the House-passed stem-cells bill, Rep. Diana DeGette (Colo.).

Earll emphasized that there is an underlying moral issue for religious conservatives. “You should not be discarding embryos that have been created. They should be implanted. There’s responsibility that comes alongside” the in vitro fertilization process, she said.