Correlation of amniotic fluid estrogens with L/S ratios and urinary estriols

17 beta-estradiol (E2) and estriol-16-glucuronide in amniotic fluid from 87 patients (normal and stressed pregnancies) were studied with radioimmunoassays. Overall, amniotic fluid estradiol and estriol increased with gestation and paralleled the increase in the L/S ratio. Statistical correlations between amniotic fluid E2 and E3 with L/S were fair and better for E3 than for E2. Correlations were better from 31 to 35 weeks of gestation than from 36 to 40 weeks. A threshold of 0.34 ng/ml should be used for E2; levels above that possibly represent fetal maturity and well-being. A threshold of 540 ng/ml should be used for E3; levels above that possibly indicate fetal maturity and wellbeing. Urine E3 correlated poorly statistically with amniotic fluid E3. Serum E3 was not studied.