A versatile radioimmunoassay for serum oestriol in pregnancy has been developed which requires 10 μ| of serum (for total) or 50 μ| (for unconjugated).
Selection of the optimum conditions for the hydrolysis of serum oestriol conjugates, the isolation of free oestriol, the displacement of tritiated oestriol by cold oestriol and the separation of the free and bound fractions is described.
Total oestriol levels doubled between weeks 34 and 38 of normal pregnancy, very little change occurring in the mean level after the 38th week of gestation. In a random series of pregnancy sera there was a significant correlation between total and unconjugated oestriol.
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