Amniotic fluid amylase concentration: a reliable predictor of fetal maturity?

The amylase concentration in the amniotic fluid (ACAF) was studied in 138 subjects in relation to duration of pregnancy, fetal weight, L/S ratios and neonatal occurrence of respiratory distress syndrome (RDS). ACAF was found to be significantly correlated with duration of pregnancy (p less than 0.001) and fetal weight (p less than 0.005). The number of false immature predictions, based on a critical value of ACAF of 200 U/l, was relatively high: 36% for the gestational age greater than or equal to 36 weeks, and 38% for fetal weight greater than 2,500 g. ACAF also showed a significant relationship with the L/S ratio (p less than 0.0001). ACAF less than 300 U/l correctly predicted all instances of L/S ratio less than 2.0; however, the rate of false low predictions was 60%. In only 22 out of 138 AF samples (16%) could the performance of an L/S ratio have been avoided on the basis of the ACAF. ACAF less than 300 U/l correctly predicted both cases of neonatal RDS in the study population; however, 1 of these fetuses had an ACAF of 260 U/l. There were four times as many false predictions of lung immaturity on the basis of ACAF less than 300 U/l as from the L/S less than 2.0.