Amniotic fluid urea nitrogen in the prediction of respiratory distress syndrome.
Amniotic fluid urea nitrogen levels can be used to predict the neonate not at risk for the development of respiratory distress syndrome. A prospective study of 110 pregnancies compared amniotic fluid urea nitrogen concentrations with the lecithin/sphingomyelin ratio and presence of phosphatidylglycerol. After determination of gestational age, amniotic fluid was analyzed for urea nitrogen concentration and an aliquot was sent to the hospital's commercial laboratory for lecithin/sphingomyelin and phosphatidylglycerol measurement. An amniotic fluid urea nitrogen level less than 7.4 mg/dl predicted the presence of neonatal respiratory distress syndrome in 12 of 13 patients independent of gestational age and birth weight. This assay can be performed at the bedside with simple equipment in 70 seconds at approximately one-fortieth the cost of present standard lung maturity studies.