Comparative Study of the Two Methods of Cervical Length Measurement in the First Trimester for the Prediction of Spontaneous Preterm Labor.

backgroundSpontaneous preterm birth remains a leading cause of neonatal morbidity and mortality worldwide. Early identification of women at risk enables timely preventive interventions. This study compared the predictive performance of one-line and two-line first-trimester transvaginal cervical length measurement methods for predicting spontaneous preterm birth.  Methods: This prospective cohort study enrolled 100 women with singleton pregnancies who attended a tertiary care hospital in Puducherry for routine first-trimester nuchal translucency screening between July 2024 and December 2025. During the 11-13+6 weeks' gestational window, transvaginal ultrasonography was used to assess cervical length using both the one-line and two-line measurement techniques. Participants were subsequently followed through pregnancy until delivery, with spontaneous preterm birth before 37 completed weeks considered the primary study outcome. The predictive performance of the two cervical length measurement methods was evaluated and compared using receiver operating characteristic (ROC) curve analysis.

resultsThe mean maternal age was 26.9±3.37 years. Most participants were aged 25-30 years (69, 69%) and multiparous (61, 61%). Spontaneous preterm birth occurred in 19 women (19%), while 81 (81%) delivered at term. Cervical length progressively decreased with earlier gestational age at delivery using both the single-line (36.3±4.22 mm, 31.4±3.35 mm, and 29.2±1.70 mm for term, 32-36+6 weeks, and <32 weeks, respectively; p<0.001) and two-line methods (39.7±4.05 mm, 34.3±3.16 mm, and 32.5±3.46 mm, respectively; p<0.001). The mean cervical length was significantly greater with the two-line method than the single-line method (38.6±4.46 mm vs. 35.3±4.52 mm; p<0.001). ROC curve analysis demonstrated superior predictive performance of the two-line method (AUC=0.860; sensitivity 82.72%; specificity 89.47%; cut-off 37 mm) compared with the single-line method (AUC=0.840; sensitivity 81.48%; specificity 89.47%; cut-off 33.7 mm).  Conclusions: Assessment of cervical length in early pregnancy is a reliable tool for predicting the risk of spontaneous preterm birth. Although both methods demonstrated good diagnostic accuracy, the two-line method showed marginally superior predictive performance and may be the preferred technique for early risk stratification and targeted preventive interventions.