Plasma and urinary oestriol during late uncomplicated pregnancy.

Plasma levels of unconjugated oestriol and urinary excretion of conjugated oestriol were measured in ten healthy women with uncomplicated late pregnancy and with normal renal function. Considerably larger differences within or between days were noted for the plasma levels than for the urinary excretion of oestriol. Significant correlation between plasma levels and urinary excretion was found in only three out of ten patients. Due to the large variations within and between days, the estimation of unconjugated oestriol in plasma might be unsuitable as a substitute for the estimation of urinary conjugated oestriol in the supervision of complicated pregnancies.