OBJECTIVE: To estimate whether cervical and lower uterine segment characteristics other than cervical length and funneling predict recurrent preterm birth. METHODS: We conducted a secondary analysis of a multicenter, blinded observational study of 181 women with singletons and prior spontaneous preterm births. Endovaginal ultrasonic examinations were performed at 2-week intervals between 16 0/7 weeks and 23 6/7 weeks of gestation. Cervical canal contour (straight/curved), cervical position (horizontal/vertical), posterior cervical width, lower uterine segment thickness, vascularity, endocervical canal dilation, with or without associated membrane prolapse and chorioamnion visible at the internal os, were systematically assessed. RESULTS: At the initial sonogram (16 0/7-18 6/7 weeks), membranes visible overlying the internal os (relative risk 1.9, confidence interval [CI] 1.2, 3.1) and canal dilation of 2-4 mm (relative risk 2.6, CI 1.4, 4.7) were significant predictors of spontaneous preterm birth of less than 35 weeks in univariate analyses. Only canal dilation remained statistically significant after controlling for cervical length (odds ratio 5.5, CI 1.1, 28.6). CONCLUSION: Endocervical canal dilation of 2-4 mm during second-trimester endovaginal sonography was associated with an increased risk of recurrent preterm delivery independent of cervical length. © 2004 by The American College of Obstetricians and Gynecologists.