The upper and lower uterine segment thickness ratio: A simple sonographic tool to triage for preterm delivery among women with threatened preterm labor

Background: Preterm delivery is a predominant cause of neonatal morbidity and mortality. Below 20% of women with threatened preterm labor, progress to active labor and delivery. Identification of such women will help to improve neonatal outcome by an early intervention such as administration of steroids and in utero transfer to the hospitals with better neonatal care. Objective: To evaluate the importance of ultrasonographic measurement of the upper and lower uterine segments thickness ratio to distinguish between true and false labor in women with threatened preterm. Methods: A prospective cohort study was carried out at a tertiary care hospital in Southern India from June 2017 to July 2018 on 151 singleton pregnant women at 24-36 weeks of gestation with regular or painful uterine contractions. Transabdominal ultrasound was performed to measure upper and lower uterine segments wall thickness and then the thickness ratio was calculated. Delivery within 7 days was the primary outcome of study. Results: Out of 151 patients, 32 (21.2%) delivered within 7 days of presentation and the rest (78.8%) delivered after 7 days and had a significant difference in the ratio of upper/lower uterine segments thickness (p<0.001). The ROC curve showed a sensitivity of 81.3% and specificity of 84.2% when the cut-off value of the thickness ratio was ≥1.61. Conclusion: The sonographic assessment of upper and lower uterine segment thickness ratio may be helpful to differentiate true labor from false labor among women with threatened preterm labor.