Ultrasonographic Transabdominal Measurement of Uterine Cervical Length for the Prediction of a Midtrimester Short Cervix

Midtrimester Cervical Length in Low-Risk Nulliparous Women for the Prediction of Spontaneous Preterm Birth: Should We Consider a New Definition of Short Cervix?

OBJECTIVE

The study aimed to estimate the predictive value of midtrimester cervical length (CL) and the optimal cut-off of CL that should be applied with asymptomatic nulliparous women for the prediction of spontaneous preterm birth (sPTB).

STUDY DESIGN

This is a prospective cohort study of asymptomatic nulliparous women with a singleton gestation. Participants underwent CL measurement by transvaginal ultrasound between 20 and 24 weeks of gestation. The participants and their health care providers remained blinded to the results of CL measurement. The primary outcomes were sPTB before 35 weeks and sPTB before 37 weeks. Receiver operating characteristics (ROC) curve analyses were performed. Analyses were repeated by using multiples of median (MoM) of CL adjusted for gestational age.

RESULTS

Of 796 participants, the mean midtrimester CL was 40 ± 6 mm with a 1st, 5th, and 10th percentile of 25, 29, and 32 mm, respectively. ROC curve analyses suggest that a cut-off of 30 mm was the optimal CL to predict sPTB before 35 weeks (area under the ROC curve [AUC]: 0.70, 95% confidence interval [CI]: 0.56-0.85) and before 37 weeks (AUC: 0.70, 95% CI: 0.59-0.80). Midtrimester CL <30 mm could detect 35% of all sPTB before 35 weeks at a false-positive rate of 5% (relative risk: 9.1, 95% CI: 3.5-23.5, p < 0.001). We observed similar results using a cut-off of CL <0.75 MoM adjusted for gestational age.

CONCLUSION

A midtrimester CL cut-off of 30 mm (instead of 25 mm), or CL less than 0.75 MoM, should be used to identify nulliparous women at high risk of sPTB.

KEY POINTS

· The optimal CL cut-off for the prediction of sPTB is 30 mm in nulliparous women.. · In nulliparous women, a midtrimester CL < 30 mm is highly associated with sPTB before 35 and 37 weeks.. · A midtrimester of CL <30 mm (5th percentile) should define a short cervix in asymptomatic nulliparous women..

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°^/7 and 21^6/7 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.