title: Accuracy of sonographic weight estimation as a function of fetal sex.
abstract: OBJECTIVE
  To determine whether the accuracy of sonographic fetal weight estimation is related to fetal sex.
  
  
  METHODS
  The accuracy of sonographic fetal weight estimation was compared between male and female fetuses using 3672 sonographic weight estimations performed within 3 days prior to delivery. Fetal weight was estimated using eight regression models that are based on different combinations of the following biometric parameters: abdominal circumference (AC), femur diaphysis length (FL), biparietal diameter (BPD) and head circumference (HC).
  
  
  RESULTS
  In seven out of the eight models tested, the presence of a male fetus was associated with a significantly lower systematic error compared with a female fetus (-0.2 to 2.1% vs. 1.3 to 6%, P<0.001). On multivariate analysis, fetal sex was independently associated with sonographic accuracy so that the likelihood of a weight estimation within 10% of birth weight was 30% higher for male fetuses compared with female fetuses. The biometric parameters that contributed most to these sex-related differences were FL and AC, while models that included HC were associated with the lowest differences in the systematic error between male fetuses and female fetuses. For most models, the random error and correlation between estimated weight and birth weight were not affected by fetal sex (8.1-12.8% vs. 8.2-13.6%, and 0.856-0.944 vs. 0.842-0.944, respectively).
  
  
  CONCLUSIONS
  Sonographic estimation of fetal weight is more accurate for male fetuses than for female fetuses. The use of sex-specific models may improve the accuracy of fetal weight estimation for female fetuses.
authors.affiliation: Helen Schneider Hospital for Women, Rabin Medical Center, Petah Tiqva, and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel. nirm@clalit.org.il
authors.forename: N
authors.initials: N
authors.lastname: Melamed
authors.forename: A
authors.initials: A
authors.lastname: Ben-Haroush
authors.forename: I
authors.initials: I
authors.lastname: Meizner
authors.forename: R
authors.initials: R
authors.lastname: Mashiach
authors.forename: M
authors.initials: M
authors.lastname: Glezerman
authors.forename: Y
authors.initials: Y
authors.lastname: Yogev
mesh_terms: D000328:Adult; D001724:Birth Weight / Q000502:physiology*; D015331:Cohort Studies; D005260:Female; D020567:Fetal Weight / Q000502:physiology*; D005865:Gestational Age; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods / Q000592:standards*; D007231:Infant, Newborn; D008297:Male; D008954:Models, Biological; D011247:Pregnancy; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D012737:Sex Factors; D016216:Ultrasonography, Prenatal / Q000379:methods / Q000592:standards*