An algorithm for determining gestational age from unconjugated estriol levels

Between the 30th and 40th weeks of gestational age (GA), plasma unconjugated estriol (E3) concentrations plotted as a logarithmic function of GA describe a complex bimodal curve. The maximum concentrations for the first peak (GAmax1) occur at approximately 34 weeks' GA, those for the second peak (GAmax2) occur at approximately 38 weeks' GA, and a between-mode nadir occurs at 35 weeks' GA. Using the close relationship between the features of this curve and GA, a computerized algorithmic curve analysis is devised for the estimation of GA during the third trimester of pregnancy. This report describes the algorithm, its clinical application, and its preliminary performance.