[1] Eunice Kennedy Shriver Natl Inst Child Hlth & Hum, Program Reprod & Adult Endocrinol, NIH, Bethesda, MD 20892 USA
[2] Shady Grove Fertil Reprod Sci Ctr, Rockville, MD USA
[3] Natl Inst Hlth Lib, Bethesda, MD USA
[4] Univ Massachusetts, Sch Publ Hlth & Hlth Sci, Div Biostat & Epidemiol, Amherst, MA 01003 USA