Plasma estrogens and pregnancy-associated plasma proteins: a study of their variability in late pregnancy.

The plasma concentration of several estrogens (unconjugated estradiol and estriol, total estriol, and estriol sulfate) and of the placental proteins hPL and PAPP-C were measured daily for 8 days in 9 subjects. The steroids showed coefficients of variation ranging from 14 to 21%. The proteins were much less variable (PAPP-C 5% and hPL 6%).