Plasma estriol vs. estrogen assays in 24-h urines as an index to fetal status

Conventionally, urinary estrogens are measured to monitor fetal well-being in the third trimester of pregnancy. There are many theoretical and practical advantages to the use of recently introduced plasma estriol assays; consequently, we undertook to compare the results of a spectrophotometric assay for total urinary estrogen with values for plasma total and free (unconjugated) estriol obtained by radioimmunoassay with commercially available kits. The data correlate well, r = 0.70 for plasma total estriol with urinary estrogen (expressed as milligrams of estrogens per gram of creatinine [E/C]), r = 0.79 for plasma free estriol with E/C, and r = 0.71 between the two plasma values. Minute-to-minute fluctuations during 90 min and day-to-day fluctuations followed during five days suggest that fluctuations of up to +/- 45% are within the normal range (means +/- SD of the day-to-day fluctuations were 16.9 +/- 7.7% and 15.6+/- 8.2%). Turn-around time is a minimum of 29 h for the urinary estrogen assay, 4.5 h for the plasma total estriol, and 3 h for the plasma free estriol.