Sonographic measurement of cervical length as a predictor of preterm delivery: a systematic review

Aim: To evaluate if transvaginal cervical length measurement in the second-trimester scan is an effective screening test for preterm delivery. Methods: We performed a search in Medline and, for each selected article, information was extracted regarding the performance of the test in terms of sensitivity, specificity, positive, and negative likelihood ratios, in low-risk, high-risk, and multiple gestations. We also evaluated the performance of the combined test (more than one sonographic marker). Results: A positive relationship was established between short cervix and preterm delivery in all articles. The majority of studies presented high specificity and positive likelihood ratio, while sensitivity and negative likelihood ratio were variable and globally poor. Better values of accuracy were found in high-risk and multiple gestations and, in all studied subgroups, for preterm delivery at lower gestational ages. Conclusions: We conclude that a short cervix is predictive of preterm delivery and can identify women that may benefit from preventive and therapeutic measures, however, a negative result is not always reassuring.