A type of cell that floats freely in the amniotic fluid of pregnant women has been found to have many of the same traits as embryonic stem cells, including an ability to grow into brain, muscle, and other tissues that could be used to treat a variety of diseases, scientists reported yesterday.

The cells, shed by the developing fetus and easily retrieved during routine prenatal testing, are easier to maintain in laboratory dishes than embryonic stem cells – the highly versatile cells that come from destroyed human embryos and are at the center of a heated congressional debate that will resume this week.

Moreover, because the cells are a genetic match to the developing fetus, tissues grown from them in the laboratory will not be rejected if they are used to treat birth defects in that newborn, researchers said. Alternatively, the cells could be frozen, providing a personalized tissue bank for use later in life.

The new cells are adding credence to an emerging consensus among experts that the popular distinction between embryonic and “adult” stem cells – those isolated from adult bone marrow and other organs – is artificial.

Increasingly, it appears there is a continuum of stem cell types, ranging from the embryonic ones that can morph into virtually any kind of tissue but are difficult to tame, up to adult ones that can turn into a limited number of tissues but are relatively easy to control.

The newly analyzed fetal stem cells, scientists said, have many of the advantages of both.

“They grow fast, as fast as embryonic stem cells, and they show great pluripotentiality,” meaning they can become many kinds of tissues, said the study leader director of the Institute for Regenerative Medicine at Wake Forest University School of Medicine in Winston-Salem, N.C, Anthony Atala. “But they remain stable for years without forming tumors,” he added, something embryonic cells are not very good at.

Dr. Atala and other scientists emphasized that they don’t believe the new cells will make embryonic stem cells irrelevant.

“There’s not going to be one shoe that fits all,” the scientific director at Advanced Cell Technology in Worcester, Mass, Robert Lanza, said. “We’re going to have to see which ones are most useful for which clinical conditions.”