Change in cervical length after arrested preterm labor and the risk of preterm birth

Abstract

Objectives:To assess the association between preterm birth and cervical length after arrested preterm labour in high-risk women.<h4>Methods</h4>In this post-hoc analysis of a randomised clinical trial, transvaginal cervical length was measured in women in whom contractions had ceased 48h after admission for threatened preterm labour. At admission, women were defined as high risk of preterm birth based on cervical length <15 mm or cervical length 15-30 mm with a positive foetal fibronectin test. Using logistic regression analysis, the association of cervical length after 48h (C2) and change in cervical length between admission (C1) and 48h later (Δc = C2-C1) was investigated with preterm birth before 34 weeks and delivery within 7 days of admission.Results: A total of 164 women were included in the analysis. Women whose cervical length (Δc) increased between admission for threatened preterm labour and 48 hours later (N=32%) were found to have a lower risk of preterm birth <34 weeks, compared to women whose cervical length did not change (odds ratio (OR) 0.24, 95% CI 0.09 to 0.69). The risk of women with a decrease in cervical length was not different (OR 1.45 95% CI 0.62 to 3.41) compared to no change in cervical length. Moreover, a longer absolute cervical length (C2) after 48 hours resulted in a lower risk of preterm birth <34 weeks and a lower risk of delivery <7 days (OR 0.90, 95% CI 0.84 to 0.96 and OR 0.91, 95% CI 0.82 to 1.02, respectively). Sensitivity analysis in women randomised to no intervention showed comparable results. Conclusions: Our study suggests that the risk of preterm birth before 34 weeks is lower when cervical length increased between admission for threatened preterm labour and 48 hours later when contractions have ceased, compared to when cervical length did not change or decreased. This article is protected by copyright. All rights reserved.