A Vatican document on bioethics maintains bans on harming embryos and on conception outside of marital intercourse, but remains open to some controversial research, including at least one technique for producing embryonic stem cells.

Dignitas Personae, "The Dignity of a Person," was issued today by the Congregation for the Doctrine of the Faith and approved by Pope Benedict XVI. It updates the last major instruction on bioethics from 1987.

"The dignity of a person must be recognized in every human being from conception to natural death. This fundamental principle expresses a great 'yes' to human life and must be at the center of ethical reflection on biomedical research," the document reads.

Archbishop Donald Wuerl of Washington, D.C., one of the U.S. bishops' experts on bioethics, said it was needed.

"Given the complexity of technology today, especially in the area of reproduction, it is not surprising that many Catholics may have confusion about the morality of a particular technology. This document provides the context for us to strengthen our teaching in this area," he said.

Bishop David Zubik of Pittsburgh said the church always has applauded science and medicine that is ethically pursued.

"This instruction reflects the church's concern, however that such research must be careful not to employ methods that violate the sacredness of human life as well as the integrity of marriage," he said.

It rejects all methods of in vitro fertilization, which is says turns babies into consumer commodities and leads to the deliberate destruction of embryos. It forbids the related freezing of embryos and experimentation on embryos. It also strongly opposes "designer babies," in which healthy embryos would be altered in an attempt to improve intelligence, strength or other qualities.

But it takes a very cautious, wait-and-see approach to research that could halt the passage of defective embryonic genes to future generations and to some proposals to produce embryonic-type stem cells without harming embryos.

"There are some issues where the document is not saying 'absolutely not," but it is saying that there are concerns here that have not been resolved and that nobody should assume it's OK given what we know now," said Richard Doerflinger, associate director for the U.S. bishops' Secretariat for Pro-life Activities.

One proposed method to create embryonic-type stem cells -- called induced pluripotent stem cells -- from adult skin cells isn't mentioned because it poses no moral problems, experts from the bishops' conference said.

"There really wouldn't be any moral objection whatsoever to how those stem cells would be obtained. How they would be used would fall under already existing principles," said Bishop William Lori of Bridgeport, Conn, chairman of the bishops' Committee on Doctrine.