A reduction in cervical length after starting vaginal progesterone in women with short cervix is significantly associated with preterm delivery ≤34 weeks and <37 weeks of gestation

ABSTRACT Objective To associate changes in cervical length (CL) after vaginal progesterone treatment with preterm delivery (PTD) Methods This is a retrospective cohort study that included 197 singleton pregnancies without (n=178) and with (n=19) history of PTD who were found to have a short cervix (≤25mm) between 18+0 and 23+6 weeks/days of gestation and subsequently had a follow up transvaginal cervical length at least one‐week after vaginal progesterone treatment started. ROC analysis was performed and three CL shortening patterns evaluated: 1) ≥10% reduction, 2) ≥20% reduction, and 3) ≥5 mm reduction in relation to the first measurement. Predictive performance for each CL reduction and associations with PTD ≤34 weeks and PTD <37 weeks were evaluated. Results Overall, prevalence of PTD ≤34 weeks was 16.7% (n=33/197), and PTD <37 weeks was 36.5% (n=72/197). The area under the ROC curve for cervical shortening and PTD ≤34 weeks was 0.703, and for PTD <37 weeks was 0.608. Prediction analysis showed sensitivity/specificity for PTD ≤34 weeks: ≤10% reduction, 48.4% and 79.8%; for ≤20% reduction, 36.4% and 87.8%; and for ≤5mm reduction, 27.3% and 83.2%, respectively; and sensitivity/specificity for PTD <37 weeks: ≤10% reduction, 36.1% and 81.6%; for ≤20% reduction, 27.8% and 90.4%; and for ≤5mm reduction, 20.8% 90.4%, respectively. The best positive likelihood ratios for PTD ≤34 and <37 weeks were for ≥20% reduction (2.98 [95% CI 1.62‐5.49] and 2.89 [1.5‐5.7], respectively. Despite significant differences in sensitivity among different cut‐off values, a reduction of ≥20% in cervical length showed the higher positive likelihood ratio and the highest association with PTD ≤34 weeks (OR 95% CI, 4.8 (2.01‐11.47)) and <37 weeks (3.63 (1.68‐7.85)), as compared to lesser reduction in cervical length. Conclusio n A reduction in cervical length in women with a short cervix treated with vaginal progesterone in a subsequent scan, can predict PTD ≤34 and <37 weeks. A ≥20% reduction had the highest positive likelihood ratio and association with preterm delivery PTD ≤34 and <37 weeks as compared to ≤10% or ≤5 mm reduction. This article is protected by copyright. All rights reserved.