title: Two-stage transvaginal cervical length screening for preterm birth in twin pregnancies.
abstract: To compare cervical length (CL) at 18-21 and 22-25 weeks' gestation in twin pregnancies in prediction of spontaneous preterm delivery and to examine cervical shortening.
  
  
  
  Retrospective cohort study of CL measured at 18-21 and 22-25 weeks' gestation in twin pregnancies.
  
  
  
  Receiver operating characteristics (ROC) curve revealed area of 0.64 (95% CI 0.53-0.75) and 0.80 (95% CI 0.72-0.88) for measurements at 18-21 and 22-25 weeks, respectively (P<or=0.001). Sensitivities of 33.3% and 23% and negative predicting value (NPV) of 97.3% and 86.8% for delivery at <28 and <34 weeks gestation were reached for measurements at 18-21 weeks. Sensitivities of 71.4% and 38.2% and NPV of 99.1% and 91.4% for delivery at <28 and <34 weeks' gestation were reached for measurements at 22-25 weeks. Cervical length shortening analysis showed an area under ROC curve of 0.81 (95% CI 0.73-0.89) and best cut-off was at >or=2 mm/week. Sensitivities of 80% and 60.8% and NPV of 98.9% and 90.6% for delivery at <28 and <34 weeks gestation were reached.
  
  
  
  In twin gestations, assessment of CL at 22-25 weeks is better than assessment at 18-21 weeks to predict preterm delivery before 34 weeks. Cervical shortening at a rate of >or=2 mm/weeks between 18 and 25 weeks gestation was a good predictor of spontaneous preterm birth in this high-risk population.
authors.affiliation: Department of Obstetrics, Hospital das Clínicas, School of Medicine, University of São Paulo, São Paulo, Brazil. hofcarol@hotmail.com
authors.forename: Carolina
authors.initials: C
authors.lastname: Hofmeister
authors.forename: Maria de Lourdes
authors.initials: Mde L
authors.lastname: Brizot
authors.forename: Adolfo
authors.initials: A
authors.lastname: Liao
authors.forename: Rossana P V
authors.initials: RP
authors.lastname: Francisco
authors.forename: Marcelo
authors.initials: M
authors.lastname: Zugaib
mesh_terms: D054791:Cervical Length Measurement / Q000706:statistics & numerical data; D002584:Cervix Uteri / Q000000981:diagnostic imaging; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011237:Predictive Value of Tests; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011272:Pregnancy, Multiple; D047928:Premature Birth / Q000000981:diagnostic imaging* / Q000209:etiology; D012189:Retrospective Studies; D012307:Risk Factors; D014427:Twins