What is predictive of preterm delivery in the first trimester: isthmus or cervical length?

Objective This study aims to evaluate the utility of first trimester cervical ultrasonography in predicting preterm delivery by separate analysis of measurements of cervical and isthmus length. Methods This is a cohort study based on data collected prospectively on singletons between 1 July 2011 and 1 February 2013. Mean cervical, isthmus and cervico-isthmic complex length were measured for deliveries before and after 37weeks. Results A total of 1494 pregnancies were analysed, including 51 cases of spontaneous preterm delivery (3.4%). The cervico-isthmic complex in the first trimester was significantly shorter in patients who delivered before term (43.8mm vs 47.5mm, p=0.04). This difference is related to differences in length at the isthmus (10.7mm vs 14.1mm, p=0.005) rather than at the cervix proper (34.5mm vs 35.0mm, p=0.56). Conclusions Measurement of the cervico-isthmic complex enables detection of a number of patients who will go on to deliver before term. Further studies are necessary to confirm that isthmic length and not cervical length is predictive of preterm delivery. (c) 2013 John Wiley & Sons, Ltd.