BACKGROUND: The usefulness of cervical length (CL) measurement in asymptomatic pregnancies in the third trimester of pregnancy is not certain. Therefore, the objective of this study was to assess the performance of CL measurement at 31-34 gestational weeks for the prediction of spontaneous late preterm birth (PTB).
MATERIALS AND METHODS: This was a prospective study of women with a singleton pregnancy, who had their routine third-trimester scan at 31-34 weeks. The CL was measured transvaginally and was tested, together with maternal demographic and obstetric parameters, for the prediction of late PTB (34 to 36 weeks), using logistic regression and ROC curve analysis.
RESULTS: Overall, from a population of 1003 women that consented to participate in the study, 42 (4.2%) delivered at 34-36 gestational weeks. A significant association was identified between gestational age at birth and CL (rho = 0.182,  < .001), and there were significant differences in the CL between cases of late preterm and term births ( < .001). Cervical length alone could predict 17% of late PTB for a 10% false positive rate, corresponding to 22 mm. A model combining CL with parity and method of conception can identify 35% of pregnancies resulting in late PTB, at a false positive rate of 10% (AUC: 0.750; 95% CI: 0.675-0.824).
CONCLUSIONS: CL assessment at 31-34 gestational weeks may contribute to the prediction of late PTB when combined with maternal characteristics.