title: Reference ranges for cervical length by transvaginal scan in singleton pregnancies.
abstract: OBJECTIVE
  The aim was to construct a chart for cervical length measured by transvaginal ultrasound.
  
  
  METHODS
  Singleton pregnant women underwent a transvaginal scan to measure the cervical length (CxL) from 20 to 34 weeks. Exclusion criteria were preterm delivery, preterm rupture of membranes, multiple pregnancies, cerclage, and those who have taken vaginal progesterone. For statistical evaluation, we used regression analysis and calculation of 5th, 50th, and 95th centiles was performed.
  
  
  RESULTS
  In the 1061 women with follow up, there were 94 (8.8%) spontaneous and 27 (2.5%) iatrogenic preterm delivery before 37 weeks. The CxL decreased with gestational age (r(2) = 0.0799). The coefficient for the interpolated median is y = 37.754 - 0.0148 x (GA)(2) + 0.2556 x (GA) (r(2) = 0.7247); for the 5th centile is y = 5.9171 - 0.0467 x (GA)(2) + 1.7059 x (GA) (r(2) = 0.6502); and for the 95th centile is y = 114.72 + 0.0758 x (GA)(2) - 4.6706 x (GA) (r(2) = 0.7783).
  
  
  CONCLUSIONS
  CxL shortened throughout the pregnancy. The chart present 5th, 50th, and 95th centile, respectively, at 23 weeks of 20 mm, 36 mm, and 47 mm; at 28 weeks of 17 mm, 33 mm, and 43 mm; and at 34 weeks of 10 mm, 29 mm, and 43 mm.
authors.affiliation: Department of Obstetrics and Gynecology, Hospital do Servidor Público Estadual de São Paulo, Francisco Morato Oliveira, São Paulo, SP, Brazil.
authors.forename: Sônia Valadares Lemos
authors.initials: SV
authors.lastname: Silva
authors.forename: Rievani
authors.initials: R
authors.lastname: Damião
authors.forename: Eduardo B
authors.initials: EB
authors.lastname: Fonseca
authors.forename: Sidney
authors.initials: S
authors.lastname: Garcia
authors.forename: Umberto G
authors.initials: UG
authors.lastname: Lippi
mesh_terms: D000328:Adult; D002584:Cervix Uteri / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D005260:Female; D005865:Gestational Age; D006801:Humans; D008137:Longitudinal Studies; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000502:physiology; D011263:Pregnancy Trimester, Third / Q000502:physiology; D012016:Reference Values; D016216:Ultrasonography, Prenatal / Q000379:methods / Q000592:standards; D014621:Vagina / Q000000981:diagnostic imaging; D055815:Young Adult