Abstract
Objective The objective of this study was to estimate the predictive value of the initial cervical
length (CL) for later CL shortening in women at high risk for recurrent spontaneous
preterm birth (SPTB).
Materials and Methods We conducted a secondary analysis of a multicenter randomized trial of high-risk
women with CL screening scheduled at least every 2 weeks from 160/7 to 226/7 weeks. Primary outcome was CL < 25 mm or SPTB before follow-up CL; the risk of this
outcome was analyzed by initial CL at 160/7 to 216/7 weeks using multivariable logistic regression and receiver operator curves.
Results A total of 786 women were identified in the parent trial; 197 (25.0%) developed CL
shortening < 23 weeks, 3 (0.4%) delivered within 2 weeks of initial CL measurement
(< 24 weeks), and 586 (74.6%) maintained CL ≥ 25 mm. The covariate-adjusted receiver
operator characteristics curve had moderate predictive value (area under the curve = 0.748)
but did not reveal a clinically useful CL cutoff. Evaluation of selected CL cutoffs
demonstrated that an initial CL ≥39 mm had the greatest negative predictive value
(85.1%). No CL cutoff existed above which there was no CL shortening, although at ≥ 39 mm
only two patients (1.1%) shortened within 2 weeks as compared with 32 (7.1%) patients
whose initial CL was < 39 mm (p < 0.001).
Conclusion In high-risk patients whose initial CL is ≥ 39 mm, CL shortening or delivery is uncommon
in the following 2 weeks. Patients with initial CL above this threshold may require
less frequent surveillance.
Keywords
cervical length shortening - predictive value - sonographic surveillance
