Evaluation of midtrimester cervical length thresholds for the prediction of spontaneous preterm birth.

INTRODUCTION

To estimate the optimal midtrimester cervical length (CL) threshold for the prediction of spontaneous preterm birth (sPTB) in asymptomatic pregnant women.

MATERIAL AND METHODS

This is a prospective observational cohort study including asymptomatic women with singleton pregnancies who underwent CL measurement by transabdominal and/or transvaginal ultrasound between 19° and 21 weeks of gestation. All CL ≤30 mm from transabdominal ultrasound were confirmed by transvaginal ultrasound. Primary outcomes were sPTB <35 and <37 weeks.

RESULTS

Out of 3,449 participants, 28 (0.8%) had a sPTB before 35 weeks and 99 (2.9%) had a sPTB before 37 weeks. Receiver operating characteristics (ROC) curves suggest that a cut-off of 30 mm was the optimal CL to predict sPTB before 35 weeks (sensitivity: 43%; specificity: 97%) and sPTB before 37 weeks (sensitivity: 21%; specificity: 97%). While a CL <25 mm was an important risk factor for sPTB before 35 weeks (relative risk: 31; 95% confidence interval: 13-73), women with a CL between 25 and 30 mm were also at greater risk (relative risk: 12; 95% confidence interval: 4 - 35) compared to women with CL ≥30 mm.

DISCUSSION

A midtrimester CL <30 mm should be considered to identify women at high-risk of sPTB.