title: Degree of fetal umbilical venous constriction at the abdominal wall in a low-risk population at 20-40 weeks of gestation.
abstract: OBJECTIVE
  To determine the degree of constriction of the umbilical vein at the abdominal wall in the second half of pregnancy.
  
  
  METHODS
  A total of 283 low-risk singleton pregnancies were recruited for a cross-sectional study, and examined once at 20-40 weeks of gestation. Two sets of ultrasound measurements of the umbilical vein were taken: one at the fetal end of the umbilical cord and another at the inlet through the abdominal wall, the umbilical ring. The diameter was determined as an average of >or=5 repeat measurements. The blood velocity was recorded at the same site.
  
  
  RESULTS
  The time-averaged maximum venous blood velocity in the cord was low (mean 13-19 cm/s during 20-40 weeks of gestation), and the corresponding mean diameter 3.6-8.2 mm. In contrast, the mean of the venous blood velocity at the umbilical ring was 34-41 cm/s and the diameter was 2.8-5.9 mm during the same period. Of 191 pairs of observations, 41 (21%) had a velocity increment of >or=300 %, which corresponds to a diameter reduction to half or more at the umbilical ring.
  
  
  CONCLUSIONS
  Constriction of the umbilical ring is a common phenomenon in the second half of pregnancy.
authors.affiliation: Department of Obstetrics and Gynaecology, Bergen University Hospital, Bergen, Norway. svein.skulstad@uib.no
authors.forename: Svein Magne
authors.initials: SM
authors.lastname: Skulstad
authors.forename: Torvid
authors.initials: T
authors.lastname: Kiserud
authors.forename: Svein
authors.initials: S
authors.lastname: Rasmussen
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D003251:Constriction, Pathologic / Q000175:diagnosis / Q000209:etiology; D003430:Cross-Sectional Studies; D005260:Female; D005333:Fetus / Q000098:blood supply* / Q000502:physiology; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D018617:Ultrasonography, Doppler, Pulsed; D016216:Ultrasonography, Prenatal; D014470:Umbilical Cord / Q000098:blood supply / Q000000981:diagnostic imaging* / Q000196:embryology; D014471:Umbilical Veins / Q000000981:diagnostic imaging* / Q000196:embryology / Q000502:physiology