Algorithmic analysis of estriol time concentration curves as a guide to timing of amniocentesis for fetal lung maturity

Utilizing a computerized algorithm which estimates gestational age (GA) by analyses of third trimester plasma estriol (E3) concentration curves, we predicted L/S ratios at the time of 64 amniocentesis indicated for assessment of fetal maturity. In the identification of immature fetuses, both methodologies concur in 95% of cases if an L/S ratio of less than or equal to 2.3 and projected GA of less than or equal to 36 weeks are accepted as cut-off points. In the identification of mature fetuses there is agreement in only 54% of cases if an L/S ratio of greater than or equal to 2.3 and projected GA of greater than or equal to 37 weeks are accepted as cut-off points. The data show that the E3 algorithm is of value in the postponing of premature and therefore unnecessary amniocenteses for fetal maturity. However the poor correlation between the E3 algorithm, a method previously shown to be accurate in GA prediction, and mature L/S ratios demonstrates the need to utilize more accurate indicators of mature amniotic fluid surfactant activity in future investigations.