Plasma unconjugated estriol as an indicator of fetal dysmaturity in postterm pregnancy.

The role of twice-weekly plasma unconjugated estriol determinations in the prediction of fetal dysmaturity was studied in 663 patients seen at the Postdates Clinic of the Los Angeles County/University of Southern California Medical Center. The correlation between estriol and gestational age was - 0.055. According to the criteria of the Postdates Clinic protocol, sensitivity, specificity, predictive values of positive results, and those of negative results of estriol determinations in predicting fetal dysmaturity were 44.4, 80.6, 32.9, and 87.1%, respectively. The major deficiency of this test for the detection of fetal dysmaturity was in the less-than-ideal predictive value of a negative result: 13% of patients who had normal estriol values had dysmature infants. When estriol was less than 12 ng/ml and the value fell more than 20% from the previous level, the predictive value of fetal dysmaturity was 56%. In these circumstances, the termination of pregnancy is a reasonable consideration. Until a more sensitive test for fetal dysmaturity is developed, plasma unconjugated estriol determination will retain its role as a screening test in managing postterm pregnancies in a large obstetric population.