Does midtrimester cervical length ≥25 mm predict preterm birth in high-risk women?

Objective: We sought to assess pregnancy outcome along a continuum of cervical lengths (CLs) ≥25 mm. Study Design: We conducted planned secondary analysis of a randomized cerclage trial of women with prior spontaneous preterm birth 17⁰-34^6/7 weeks. Outcomes of women who maintained CLs ≥25 mm were analyzed. Women with CLs <25 mm randomized to no cerclage comprised an internal comparison group. Results: Of 1014 screened, 153 had CL <25 mm, and 672 had CL ≥25 mm. Birth <35 weeks occurred in 16% of the ≥25 mm cohort. The relationship between CLs ≥25 mm and birth gestational age was null (P = .15). In the <25 mm group, progressively shorter CLs predicted birth <35 weeks (P < .001); this relationship was null in the ≥25 mm group (P = .17). Conclusion: The continuum of CLs ≥25 mm measured between 16^0/7-22^6/7 weeks does not predict gestational length in women with prior spontaneous preterm birth.