title: Role of fetal length in the prediction of fetal weight.
abstract: OBJECTIVE
  The purpose of this study was to compare the accuracy of routine fetal biometric indices in the prediction of fetal length and to determine whether more accurate sonographic measures of fetal length can improve the accuracy of fetal weight estimation.
  
  
  METHODS
  The accuracy of the common sonographic fetal biometric indices for predicting fetal length was determined using 3689 sonographic weight estimations performed within 3 days before delivery. The fetal length at the time of the sonographic examination was assumed to be equal to the neonatal length, which is routinely measured within 24 hours of delivery. Two new regression models for fetal weight estimation, one with and one without fetal length as an independent variable, were generated to determine the potential contribution of more accurate predictors of fetal length to the accuracy of fetal weight estimation.
  
  
  RESULTS
  Abdominal circumference was a significantly more accurate predictor of fetal length (r = 0.732) compared with femur length (r = 0.712), biparietal diameter (r = 0.644), and head circumference (r = 0.661; P < .05), although each of these biometric indices explained only about 50% of the variance in fetal length (R(2) = 0.423-0.548). The addition of fetal length as an independent variable to a birth weight prediction model significantly improved the model's correlation with birth weight(r = 0.917 versus 0.903; P = .006), systematic error (0.2% versus 0.6%; P < .001), random error (6.7% versus 7.5%; P < .001), mean absolute percent error, and the proportion of estimations within 5% and 10% of birth weight.
  
  
  CONCLUSIONS
  The correlation between routine biometric indices and fetal length is limited. Identification of new fetal sonographic biometric indices with greater predictive accuracy for fetal length may improve the accuracy of fetal weight estimation.
authors.affiliation: Department of Obstetrics and Gynecology, Helen Schneider Hospital for Women, Rabin Medical Center, 49100 Petah Tiqwa, Israel. nirm@clalit.org.il
authors.forename: Nir
authors.initials: N
authors.lastname: Melamed
authors.forename: Yariv
authors.initials: Y
authors.lastname: Yogev
authors.forename: Nechama
authors.initials: N
authors.lastname: Linder
authors.forename: Zeev
authors.initials: Z
authors.lastname: Efrat
authors.forename: Ron
authors.initials: R
authors.lastname: Bardin
authors.forename: Arnon
authors.initials: A
authors.lastname: Wiznitzer
authors.forename: Israel
authors.initials: I
authors.lastname: Meizner
mesh_terms: D000328:Adult; D001699:Biometry / Q000379:methods; D018568:Crown-Rump Length; D005260:Female; D020567:Fetal Weight; D005333:Fetus / Q000033:anatomy & histology*; D005865:Gestational Age; D006801:Humans; D011237:Predictive Value of Tests; D011247:Pregnancy; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D016216:Ultrasonography, Prenatal