Characterization of the 21-yl sulfates of 11-beta, 17-alpha,21-trihydroxypregn-4-ene-3,20-dione; 17-alpha,21-dihydroxypregn-4-ene-3, 11,20-trione; 11-beta,21-dihydroxyregn-4-ene-3,20-dione; 21-hydroxypregn-4-ene-3, 11,20-trione and 21-hydroxypregn-4-ene,3,20-dione in human cord plasma.