Clinical Application of amino-terminal pro-brain natriuretic peptide (NT-proBNP) concentration in amniotic fluid for the Prediction of Preterm Birth in Symptomatic Women

Background Preterm birth accounts for 60-80% of neonatal mortality. Approximately one-third of preterm births are caused by the spontaneous onset of preterm labor. Nevertheless, 70%-90% of women diagnosed with preterm labor will not deliver within seven days. Thus, many women will be unnecessarily treated by preterm labor with risk medications. Better tools are needed to categorize women in preterm labor into high or low risk of preterm delivery. Objective To evaluate the amino-terminal pro-brain natriuretic peptide concentration in the amniotic fluid as a prognostic test to predict the risk of delivery within 48 h or 7 days and before 34+0 or 37+0 weeks in women in preterm labor. Study Design 102 pregnant women presenting signs and symptoms of spontaneous preterm birth (22+0 to 34+0 weeks of gestation) were included. Amniotic fluid was obtained by amniocentesis, and amino-terminal pro-brain natriuretic peptide concentration was measured. Below normal concentration was defined as < 0.5 multiples of the median of the standard curve according to gestational age. We estimated the risk of preterm delivery risk according to normal or lower-than-normal concentrations of amino-terminal pro-brain natriuretic peptide. The predictive capacity of the test (below normal concentration of amino-terminal pro-brain natriuretic peptide) was evaluated to identify spontaneous preterm birth at 48 h or 7 days from amniocentesis, and less than 34+0 or 37+0 weeks at delivery. Results For the outcome delivery within 48 h, lower than normal amino-terminal pro-brain natriuretic peptide concentration had 94.6% sensitivity, 73.8% specificity, 96% negative predictive value, and positive and negative likelihood ratios 3.6 and 0.07, respectively. For the outcome delivery within 7 days, the test had 93.9% sensitivity, 88.7% specificity, 94% negative predictive value, and positive and negative likelihood ratios 8.3 and 0.07, respectively. For the outcome of spontaneous preterm birth before 34+0 and 37+0 weeks, below normal amino-terminal pro-brain natriuretic peptide had 80% sensitivity, 83% specificity, 78% negative predictive value, positive and negative likelihood ratio 4.7 and 0.24 and 64.1% sensitivity, 91.7% specificity, 44% negative predictive value, positive and negative likelihood ratio 7.7 and 0.39 respectively. Conclusion Among patients in spontaneous preterm labor, the detection of lower-than-normal concentrations of amino-terminal pro-brain natriuretic peptide (< 0.5 multiples of the median) in amniotic fluid has an excellent predictive capacity to identify those patients at low risk of preterm delivery within 48 h or 7 days.