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

Abstract

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 17(0)-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.

Figure 1. Flow of participants

Figure 2. Relationship between cervical length groups and birth < 35 weeks

Rates of preterm birth < 35 weeks by cervical length group in both the < 25 mm, no-cerclage, internal comparison cohort and ≥ 25 mm, failed-to-shorten cohort

Figure 3. Kaplan-Meier survival curves of cervical length groups

Probability of delivery across gestation in the ≥ 25 mm cohort, comparing women with cervical lengths 25–29 mm and those with cervical lengths 30 mm or greater.