Determination of amniotic fluid microviscosity at body temperature: a predictor of fetal lung maturity

One of the most convenient ways to determine fetal lung maturity is by measuring the fluorescence polarization (P) of the amniotic fluid at room temperature. With sensitivity fixed on 100%, specificity is relatively unsatisfactory. The present study compared the predictive power of fluorescence polarization measured at temperatures 25C (P25), 37C (P37), and 40C (P40) among 195 consecutive samples tested at both 25C and 37C, with a subgroup of 86 samples tested also at 40C. A better separation between the results for fetuses with and without hyaline membrane disease is attained at P37, demonstrated by a greater mean standardized distance (distance between P values for those patients with and the mean P value for those patients without hyaline membrane disease in unit of standard deviation of the latter; 1.597 +/- 0.528 for P25 versus 2.332 +/- 0.591 for P37). Fixing the sensitivity at 100%, the specificity of P25 and P37, were 68.9 and 94.9%, respectively; a highly significant difference (P less than .001). The specificity of P40 was 90.5%, lower than that of P37. P37 is the best predictor and adding either P25 or P40 does not improve the prediction of lung maturity. It is concluded that P37 should replace P25 as the definite index for fetal lung maturity.