Diurnal variations in unconjugated plasma and total urinary estriol levels in late normal pregnancy.

Diurnal variations in plasma unconjugated estriol and urinary estriol were assessed in 12 pregnant women during the 3rd trimester of uncomplicated pregnancies. Commercially available 125I-labelled radioimmunoassay kits were used. The preliminary data presented here support the hypothesis that there is no circadian rhythm of unconjugated plasma estriol in normal late pregnancy. Total urinary estriol reaches a nadir during the sleep hours (24.00-6.00). A biological carrier 'stick' for estriol measurements might serve as test of choice in the monitoring of high-risk pregnancy as well as for identifying pregnancies complicated by chromosomal abnormalities (e.g., Down's syndrome).