Preterm birth (PTB) is defined as a birth that occurs before 37 weeks of gestation, which is the leading cause of perinatal morbidity and mortality. 1 The inherent cervical length and strength are two main features of the cervix that determine whether a pregnant woman is at risk for spontaneous PTB. 2 A short cervix identified by transvaginal ultrasound in the second trimester of pregnancy is associated with a significant risk of spontaneous PTB. It is recognized that the measurement of cervical length in the second trimester can identify high-risk women that may benefit from progesterone prophylaxis. 3,4 However, the low sensitivity and positive predictive value have limited the clinical utility of cervical length assessment as a universal screening tool. 5-7 In the first trimester of pregnancy, the presence of the undeveloped lower uterine segment and the variable degree of the curvature of the endocervical canal have generated significant technical challenges for the cervical length to be measured, which

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Introduction Our objectives were to compare the single‐line and two‐line methods of cervical length measurement in the first trimester of pregnancy and to evaluate the potential value of the first trimester cervical length measured by the two methods in predicting spontaneous preterm birth. Material and methods This was a prospective study in singleton pregnancies at 11+0 to 13+6 weeks of gestation. Cervical length was measured by two methods: (i) a linear distance between the two ends of the glandular area around the endocervical canal (single‐line method) and (ii) a sum of a linear distance from the internal os to the greatest cervical curvature and a linear distance from this point of the cervix to the external os (two‐line method). The screening performance of the first trimester cervical length measured by the two different methods for the prediction of spontaneous preterm delivery was assessed by receiver‐operating characteristics (ROC) curve analysis. The areas under the ROC (AUROC) were compared by De Long test. Results A total of 1484 consecutive singleton pregnancies were included in this study. Spontaneous preterm delivery at <37 and <32 weeks occurred in 75 cases (5.1%) and 12 cases (0.8%), respectively. The median cervical length measured by the single‐line method was significantly shorter than that by the two‐line method (33.5 vs 36.5 mm, p < .001). Compared with the term delivery group, the median cervical length measured by the two‐line method was shorter in women with spontaneous delivery at <32 weeks of gestation (36.5 vs 33.6 mm, p < .01). No significant difference in the median cervical length measured by the single‐line method was detected between the spontaneous preterm delivery and term delivery groups. Receiver‐operating‐characteristic curves demonstrated that cervical length measured by the two‐line method achieved better performance in predicting spontaneous delivery at <32 weeks compared with the single‐line method (AUROC: 0.72 vs 0.61, p < .01). Conclusions We have demonstrated that the first trimester cervical length, measured by the two‐line approach, holds promise as a potential screening tool for early spontaneous preterm delivery.