50 Top 10 Lists of 2007

Top 10 Medical Breakthroughs

#9. New Source of Stem Cells

This was a banner year for stem-cell research. But one advancement that may not have had its due was the discovery of stem cells in amniotic fluid. Researchers believe that amniotic fluid–derived stem cells, AFS for short, have the potential to give rise to many, but perhaps not all, of the 220 specialized cell types found in the human body — placing the potential usefulness of AFS cells somewhere between embryonic and adult stem cells. Best of all, AFS cells are easy to come by. They're bountiful in fluid specimens left over from amniocentesis, a common prenatal procedure that extracts amniotic fluid to test for genetic disorders; another ready source of AFS cells may be "afterbirth," the tissue new mothers lose after childbirth. Considering that four million babies are born in the United States each year, AFS cells are sure to draw much future research.

Connect to this TIME Story