Daily variation of serum unconjugated estriol and estetrol in normal pregnancy.

Serum unconjugated estriol and estetrol were assayed daily in seven nondiabetic, uncomplicated third-trimester pregnancies to define the daily variation of these compounds. When compared to the mean of the three preceding days' values, or to the highest mean of three consecutive daily values previously obtained in a pregnancy, daily estriol and estetrol values fell greater than or equal to 40% on 1.2 and 0% of occasions, respectively. Isolated estriol values represented falls of greater than or equal to 40% from previously obtained single estriol values on 2% of occasions, and no isolated estetrol values fell greater than or equal to 40% from any other isolated values obtained in a given pregnancy. These results define the stability of daily serum estriol and estetrol in late-gestation normal pregnancy, although they emphasize the large variability encountered when comparing isolated estriol values.