- Objective The aims of the study were to determine cervical length among patients with polyhydramnios and to assess the relationship between the severity of polyhydramnios, cervical length and gestational age at delivery. Patients and methods A prospective study was designed including 92 consecutive singleton pregnancies with polyhydramnios between 24 and 40 weeks' gestation. Cervical length was measured using transvaginal sonography. Polyhydramnios was defined when amniotic fluid index (AFI) was equal to or greater than 20 cm. A single sonologist performed all the examinations of the cervical length and the AFI. Results The median cervical length and AFI were 37.5 (range, 7–52) mm and 28.8 (range, 20–43) cm, respectively. A significant gradual shortening of the cervical length was observed with advancing gestational age (P = 0.027). No significant association was found between AFI and cervical length (P = 0.24). A cut-off of 15 mm (n = 5) was associated with a significantly lower gestational age at delivery (30 ± 2.6 weeks vs. 37.2 ± 4.2 weeks, respectively, P < 0.001). Conclusions Women with polyhydramnios have a gradual shortening of cervical length with advancing gestational age. However, this finding is not related to the severity of polyhydramnios. Copyright © 2006 ISUOG. Published by John Wiley & Sons, Ltd.