title: Reference data representative of normal findings at three-dimensional power Doppler ultrasound examination of the cervix from 17 to 41 gestational weeks.
abstract: OBJECTIVE
  To develop normal reference ranges for cervical volume and vascular indices using three-dimensional (3D) power Doppler ultrasonography from 17 to 41 gestational weeks.
  
  
  METHODS
  This was a cross-sectional study of 352 nulliparous and 291 parous women who delivered at term and underwent transvaginal 3D power Doppler ultrasound examination of the cervix once at 17 to 41 weeks' gestation. We examined approximately 25 women in each gestational week. Cervical volume, vascularization index (VI), flow index (FI) and vascularization flow index (VFI) were calculated.
  
  
  RESULTS
  There was no change in cervical volume between 17 and 40 weeks' gestation. At 41 weeks cervical volume was slightly smaller than it was at 17-40 weeks (P=0.03 for nulliparous women and P=0.08 for parous women). The cervical volume was larger in parous than it was in nulliparous women (median 38 cm3 vs. 32 cm3 at 17-40 weeks, P<0.0001; median 31 cm3 vs. 22 cm3 at 41 gestational weeks, P=0.288). FI did not differ between nulliparous and parous women and remained unchanged between 17 and 41 weeks' gestation (median 30.6, range 21.2-55.2). VI and VFI did not change consistently from 17 to 41 weeks, but the values were higher in parous than they were in nulliparous women at 17-30 weeks (median VI 5.3% vs. 3.1%, P<0.0001; median VFI 1.6 vs. 0.9, P<0.0001). At 31-41 gestational weeks the median VI for all women irrespective of parity was 4.9% and the median VFI was 1.4.
  
  
  CONCLUSIONS
  Reference values for cervical volume and blood flow indices as assessed by 3D power Doppler ultrasonography have been established for the second half of pregnancy. These lay the basis for studies of pathological conditions.
authors.affiliation: Obstetric, Gynecological and Prenatal Ultrasound Research Unit, Department of Clinical Sciences, Malmö, Lund University, and Department of Obstetrics and Gynecology, Malmö University Hospital, Malmö, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Rovas
authors.forename: P
authors.initials: P
authors.lastname: Sladkevicius
authors.forename: E
authors.initials: E
authors.lastname: Strobel
authors.forename: L
authors.initials: L
authors.lastname: Valentin
mesh_terms: D000293:Adolescent; D000328:Adult; D001783:Blood Flow Velocity; D002584:Cervix Uteri / Q000033:anatomy & histology / Q000098:blood supply / Q000000981:diagnostic imaging*; D003430:Cross-Sectional Studies; D005260:Female; D047109:Fetal Development; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data; D010298:Parity; D011247:Pregnancy; D011264:Pregnancy Trimesters; D012016:Reference Values; D016216:Ultrasonography, Prenatal