Time trend analysis of unconjugated estriol concentrations in third-trimester pregnancy

Utilizing a plasma pooling procedure to control short-term pulsatile variability of unconjugated estriol (E3) concentrations, the authors evaluated time trend curves in 42 subjects after normalizing time trend curves in 42 subjects after normalizing gestational age (GA) by a computerized algorithm. Semilogarithmic plots from individual subjects and a median plot derived from pooling the 42 subjects describe complex bimodal curves beginning with an initial steep rise at 30 to 32 weeks' GA, a peak between 32 and 34 weeks' Ga, a transient nadir at 35 weeks' GA, a second steep rise between 35 and 37 weeks' Ga, a second peak between 37 and 39 weeks' Ga, and a downward segment just prior to parturition. Predicted GAs at delivery obtained from individual curve analyses concurred with pediatric GAs within 2 weeks or less in 41 or 42 pregnancies.