The uterocervical angle-cervical length ratio: A promising predictor of preterm birth?

Objective: To predict spontaneous preterm birth (sPTB) (labor before 37 weeks of pregnancy) in low-risk singleton pregnancies during the second trimester, using ultrasound markers: uterocervical angle (UCA) and cervical length (CL).

Methods: In a prospective observational cohort study, we followed primigravid women with singleton pregnancies without known risk factors for sPTB from 1623 weeks of pregnancy until birth. Transvaginal ultrasonography on admission revealed the UCA and CL, and maternal history was obtained from submitted patient profiles. Logistic regression models disclosed significant predictive variables, and receiver operating curves (ROCs) demonstrated optimal cut-offs and test accuracy indices. Predictive functions of variables were compared using positive and negative likelihood ratios.

Results: In a sample of 357 participants, 41 (11.5%) experienced sPTB. UCA and CL were significantly associated with sPTB when adjusting for other variables (adjusted odds ratio: UCA 1.05, 95% confidence interval [CI] 1.02-1.07 and CL 0.82, 95% CI 0.75-0.90). Optimal cut-offs were estimated to be 106° and 33 mm for UCA and CL, respectively. We devised the novel index UCA/CL with an area under the ROC of 0.781 (95% CI 0.734-0.823), cut-off = 3.09°/mm, and improved likelihood ratios (positive: 3.18, 2.47, and 4.22; negative: 0.63, 0.52, and 0.51 for UCA, CL, and UCA/CL, respectively).

Conclusion: The second-trimester UCA/CL was found to be a promising index to predict sPTB in low-risk singleton pregnancies. Further multicenter studies may generalize this conclusion to other gestational ages or risk groups and make it more comprehensive by considering other risk factors.