[1] UNIV PENN, DEPT OBSTET & GYNECOL, PHILADELPHIA, PA 19104 USA
[2] UNIV PENN, DEPT PATHOL, PHILADELPHIA, PA 19104 USA
[3] UNIV PENN, DEPT LAB MED, PHILADELPHIA, PA 19104 USA
[4] UNIV PENN, DEPT INTERNAL MED, PHILADELPHIA, PA 19104 USA
[5] MED COLL PENN, DEPT BIOCHEM & PHYSIOL, PHILADELPHIA, PA 19129 USA