title: Relationship between cerebroplacental Doppler ratio and birth weight in postdates pregnancies.
abstract: OBJECTIVE
  To explore the relationship between cerebroplacental Doppler impedance index and birth weight in postdates pregnancies, and to evaluate the use of a combination of Doppler parameters and ultrasound biometry in the prediction of large-for-gestational age (LGA) fetuses at 41 weeks of gestation.
  
  
  METHODS
  The pulsatility indices of the umbilical (UA-PI) and middle cerebral (MCA-PI) arteries, the cerebroplacental pulsatility index ratio (CPR) and the estimated fetal weight (EFW) were obtained in a cohort of 181 ultrasound-dated pregnancies at 41 weeks' gestation, 2 days before induction of delivery. A regression equation was established and the correlation between umbilical artery impedance and different birth-weight centile groups was determined. A receiver-operating characteristics (ROC) curve was used to compare prediction of LGA fetuses using biometry alone with that using biometry and UA-PI.
  
  
  RESULTS
  UA-PI was inversely related to EFW (Spearson's correlation coefficient rho = -0.28, P < 0.001). Logistic regression showed an independent contribution of UA-PI to the birth-weight estimation (birth weight = 1356.8 - 232.0 x UA-PI + 0.65 x EFW). On ROC curve analysis, the prediction of LGA with the regression equation was comparable to that using ultrasound biometry alone.
  
  
  CONCLUSIONS
  UA-PI was inversely correlated to EFW, but the combination of ultrasound biometry and UA-PI compared with biometry alone showed similar prediction of LGA fetuses in postdates pregnancies. Further prospective trials on larger populations or groups with a higher prevalence of LGA fetuses would be needed to validate the use of the new formula.
authors.affiliation: Department of Obstetrics and Gynaecology, University of Hong Kong, HKSAR, China. lamswh@yahoo.com.hk
authors.forename: H
authors.initials: H
authors.lastname: Lam
authors.forename: W C
authors.initials: WC
authors.lastname: Leung
authors.forename: C P
authors.initials: CP
authors.lastname: Lee
authors.forename: T T
authors.initials: TT
authors.lastname: Lao
mesh_terms: D000328:Adult; D001724:Birth Weight; D005260:Female; D005320:Fetal Macrosomia / Q000000981:diagnostic imaging*; D006801:Humans; D007231:Infant, Newborn; D007233:Infant, Postmature; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011673:Pulsatile Flow; D012372:ROC Curve; D012044:Regression Analysis; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric; D018608:Ultrasonography, Doppler; D016216:Ultrasonography, Prenatal; D014469:Umbilical Arteries / Q000000981:diagnostic imaging*