title: Cervical length at 11-40 weeks: unconditional and conditional longitudinal reference ranges.
abstract: BACKGROUND
  Our aim was to establish unconditional and conditional longitudinal reference ranges for cervical length throughout pregnancy.
  
  
  METHODS
  Prospective longitudinal study. In singleton pregnancies repeated cervical length measurements were carried out by transvaginal ultrasound throughout gestation. Multilevel modeling was applied to establish cervical length reference ranges from 11 to 40 weeks.
  
  
  RESULTS
  In all, 4397 women contributed to 13 765 cervical length measurements. A linear mixed effects random intercept-random slope model was fitted to the data. Mean cervical length had a negative non-linear polynomial association with gestational age. Unconditional ranges were developed. Terms that allow the construction of personalized cervical length charts conditional to a previous measurement were calculated.
  
  
  CONCLUSIONS
  We constructed longitudinal reference charts for cervical length in singleton pregnancies. Cervical length should be adjusted according to specific gestational-age-dependent ranges. Individualization of cervical assessment is feasible by the application of charts conditional to previous measurements.
authors.affiliation: Fetal Medicine Unit, Leto Maternity Hospital, Athens, Greece.|Emvryomitriki, Fetal Medicine Unit, Athens, Greece.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Papastefanou
authors.affiliation: Fetal Medicine Unit, Leto Maternity Hospital, Athens, Greece.|Emvryomitriki, Fetal Medicine Unit, Athens, Greece.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Pilalis
authors.affiliation: Emvryomitriki, Fetal Medicine Unit, Athens, Greece.
authors.forename: Dimitra
authors.initials: D
authors.lastname: Kappou
authors.affiliation: Fetal Medicine Unit, Leto Maternity Hospital, Athens, Greece.|Emvryomitriki, Fetal Medicine Unit, Athens, Greece.
authors.forename: Athena P
authors.initials: AP
authors.lastname: Souka
mesh_terms: D000328:Adult; D054791:Cervical Length Measurement; D002584:Cervix Uteri / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D005865:Gestational Age; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D011247:Pregnancy / Q000502:physiology*; D011264:Pregnancy Trimesters / Q000502:physiology; D011446:Prospective Studies; D012016:Reference Values
keywords: Cervix; longitudinal ranges; multilevel modeling; pregnancy; preterm birth; transvaginal ultrasound