title: The effect of umbilical venous constriction on placental development, cord length and perinatal outcome.
abstract: BACKGROUND
  Umbilical vein constriction at the fetal abdominal inlet is a common finding after week 13, when the period of umbilical herniation is brought to an end.
  
  
  OBJECTIVE
  To test the hypothesis that a constricting umbilical ring within physiological ranges affects fetal hemodynamics by either pooling blood in the placenta or restricting nutrient transfer to the fetus and thus shift the birthweight/placental weight (BW/PW) ratio. A constriction could also cause pressure changes and elongation of the cord and possibly be a disadvantage during labour.
  
  
  METHODS
  Cross-sectional.
  
  
  METHODS
  359 Low-risk singleton pregnancies at 13-40 weeks of gestation.
  
  
  METHODS
  Standard deviation score (z-score) and regression analysis were used to determine the effect of umbilical vein constriction (expressed by increased blood velocity) on birthweight/placental weight ratio (BW/PW), cord length, Apgar score and emergency delivery due to fetal distress.
  
  
  RESULTS
  Umbilical venous constriction had a mild but significant effect on BW/PW in male (p=0.018) but not in female fetuses. Increased constriction was also associated with increased length of the cord but only in female fetuses (p=0.019). Cord length was positively related to birthweight and placental weight, but an increased length of the cord was also associated with decreasing BW/PW ratio for the male fetuses only (p=0.044). Increasing degree of venous constriction was associated with Apgar score < or =7 at 1 (p=0.009) but not at 5 min after birth and was not associated with emergency delivery.
  
  
  CONCLUSIONS
  Physiological umbilical venous constriction exerts a mild but significant gender-specific hemodynamic impact on intrauterine development.
authors.affiliation: Institute of Clinical Medicine, Department of Obstetrics and Gynaecology, University of Bergen, Bergen, Norway. svein.skulstad@uib.no
authors.forename: Svein Magne
authors.initials: SM
authors.lastname: Skulstad
authors.forename: Svein
authors.initials: S
authors.lastname: Rasmussen
authors.forename: Silje
authors.initials: S
authors.lastname: Seglem
authors.forename: Ragnhild H
authors.initials: RH
authors.lastname: Svanaes
authors.forename: Hanne May
authors.initials: HM
authors.lastname: Aareskjold
authors.forename: Torvid
authors.initials: T
authors.lastname: Kiserud
mesh_terms: D000293:Adolescent; D000328:Adult; D001034:Apgar Score; D001724:Birth Weight; D001783:Blood Flow Velocity; D003250:Constriction; D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D009929:Organ Size; D010920:Placenta / Q000033:anatomy & histology; D010929:Placentation / Q000502:physiology*; D011247:Pregnancy; D011256:Pregnancy Outcome; D012044:Regression Analysis; D012737:Sex Factors; D014470:Umbilical Cord / Q000033:anatomy & histology*; D014471:Umbilical Veins / Q000502:physiology*