Nitric oxide metabolite levels and assessment of cervical length in the prediction of preterm delivery among women undergoing symptomatic preterm labor.

OBJECTIVE: To evaluate the diagnostic accuracy of measuring cervical length (CL) in combination with cervical and plasma nitric oxide metabolite (NOx) levels to identify women undergoing preterm labor (PTL) who will deliver preterm. METHODS: A hospital-based prospective cohort study of 730 women undergoing spontaneous PTL between 24 and 33weeks+6days of pregnancy was conducted. Measurement of cervical and plasma NOx levels and ultrasonographic assessment of CL were performed to find the best model to predict preterm delivery (PTD). Optimal cut-off values were calculated by receiver operating characteristic (ROC) curve analysis. Logistic regression analysis and rank correlation tests were also performed. RESULTS: CL of 15mm or less, cervical NOx levels greater than 87.6μmol/L, and plasma NOx levels greater than 123μmol/L (P<0.0001) were the only factors significantly associated with PTD within 7days of sampling. This combined model provided high diagnostic accuracy (sensitivity 80.0\%; specificity 99.2\%). Both cervical and plasma NOx levels were negatively correlated with CL (r=-0.453, P<0.0001 and r=-0.362, P<0.0001, respectively). CONCLUSION: Combined measurement of CL and levels of cervical and plasma NOx could help identify women undergoing symptomatic PTL who are at increased risk of PTD.