Follow-Up of Asymptomatic High-Risk Patients with Normal Cervical Length to Predict Recurrence of Preterm Birth.

BACKGROUND: A midtrimester cervical length (CL) <25 mm is associated with spontaneous preterm birth (sPTB). However, as CL ≥25 mm is not enough to exclude recurrence in high-risk patients, follow-up CL measurement later in pregnancy has been proposed. OBJECTIVES: To evaluate whether CL measurement at 26±1 weeks in asymptomatic high-risk patients improves the prediction of sPTB recurrence. METHODS: A retrospective cohort of high-risk women because of previous sPTB was analyzed. Patients with a CL ≥25 mm at 20±1 weeks and subsequent CL measurement at 26±1 weeks were included. The exclusion criteria were incomplete follow-up, any treatment before CL assessments, and medically indicated preterm birth. The association and predictive performance of CL at 26±1 weeks for sPTB was studied. RESULTS: Of 131 patients with a CL measurement at 26±1 weeks, 19 and 4.6% presented sPTB before 37 and 34 weeks, respectively. The rate of sPTB before 37 weeks was higher in women with a CL <25 mm (37.5 vs. 16.5%, RR 2.3 [1.07-4.8], p = 0.045), although the detection rate of CL at 26±1 weeks to predict sPTB before 37 weeks was 24% (95% CI 10-46%). The performance did not improve regardless of the selected cutoff. CONCLUSIONS: In asymptomatic high-risk patients, CL <25 mm at 26±1 weeks is associated with higher risk of sPTB. However, the prediction of recurrence by CL was low and did not improve, regardless of the selected cutoff.