Maternal serum unconjugated estriol and urine estriol concentrations in normal and high-risk pregnancy.

Serum unconjugated estriol levels and urinary estriol levels of concurrent specimens were compared for 6 normal and 6 high-risk subjects throughout the last trimester of pregnancy. Free estriol values in serum exhibited a close correlation with urinary estriol values for both the normal (r = 0.91) and high-risk (r = 0.92) groups. The results of this study indicate that the assessment of high-risk pregnancies now accomplished principally by urinary estriol assays may be performed by more convenient and rapid radioimmunoassays developed for quantification of free estriol in serum.