Purpose: to establish a reference range for cervical length measurement throughout gestation in twin pregnancies and to correlate cervical length with gestational age at delivery. Methods: retrospective analysis of prospectively collected data between 1994 and 2000, involving 149 twin pregnancies undergoing transvaginal ultrasound examination every four weeks for measurement of cervical length. Results: one hundred and twenty-seven women (85.2%) delivered after 34 weeks, 20 (13.4%) between 24 and 33 weeks and two pregnancies resulted in fetal loss before 24 weeks. The mean gestational age at delivery was 36.3 weeks. A total of 497 ultrasound examinations with cervical length measurement were performed in 127 patients with twin pregnancies who delivered after 34 weeks (mean = 4 examinations per patient). All scans were carried out between 9 and 39 weeks (mean = 29.4 weeks). There was an inverse correlation between cervical length measurement and gestational age at the scan in twin pregnancies (r=-0.44; p < 0.0001). The mean value was 44 mm at 10 weeks and 28 mm at 36 weeks. The corresponding fifth percentile values of these gestations were 28 mm and 12 mm, respectively. Cervical length measurement changes were more pronounced in the second half of the pregnancy (Kruskal-Wallis test, p=0.0006). Mean cervical length measurement and 90% prediction interval values were established throughout gestation by regression analysis. Twenty-six cases delivered before 34 weeks, nine of these cases (34.6%) had at least one cervical length measurement below the 5th percentile. Conclusions: cervical length shortens gradually throughout gestation in twin pregnancies but changes are more significant in the second half of the pregnancy. Approximately one-third of the pregnancies that delivered before 34 weeks had at least one cervical length measurement below the 5th percentile for the gestational age.
Twin Pregnancy; Cervical length measurement; Prematurity
