title: Sonographic estimation of fetal head circumference: how accurate are we?
abstract: OBJECTIVE
  To assess the accuracy of sonographic estimation of fetal head circumference (HC).
  
  
  METHODS
  We compared sonographic estimations of fetal HC with actual measurements performed immediately after delivery using 3008 sonographic examinations performed within 3 days prior to delivery. The following measures of accuracy were calculated: correlation with actual HC, systematic error, random error, simple error, mean absolute percentage error and fraction of estimates within 5% of actual HC. Multivariate logistic regression analysis was used to identify factors affecting the accuracy of sonographic HC estimation.
  
  
  RESULTS
  There was a high correlation between sonographic and postnatal measurements of HC (r = 0.845, P < 0.001). Overall, sonographic HC measurements consistently underestimated actual HC measured postnatally (mean simple error, - 13.6 mm; 95% CI, - 13.2 to - 13.9), and the difference increased with gestational age. A high cephalic index (> 0.81) (odds ratio (OR), 0.3; 95% CI, 0.2-0.4), HC > 90(th) centile (OR, 0.5; 95% CI, 0.3-0.6), delivery by vacuum extraction (OR, 0.6; 95% CI, 0.4-0.8), gestational week (OR, 0.7; 95% CI, 0.6-0.9) and male fetal gender (OR, 0.8; 95% CI, 0.6-0.9) were associated with decreased sonographic accuracy. At term, breech presentation at the time of sonographic examination was associated with a higher sonographic accuracy compared with vertex presentation (-12.0; 95% CI, - 10.5 to - 13.5 vs. - 13.9 mm; 95% CI, - 13.6 to - 14.3; P = 0.02). The random error was relatively constant, and was unaffected by any of the obstetric factors studied.
  
  
  CONCLUSIONS
  Sonographic estimation of HC is associated with significant underestimation compared with the actual postnatal HC. This measurement error may have important clinical implications and should be taken into account in the interpretation of sonographically measured HC.
authors.affiliation: Department of Obstetrics and Gynecology, Helen Schneider Hospital for Women, Rabin Medical Center, Petach Tikva 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: Y
authors.initials: Y
authors.lastname: Yogev
authors.forename: D
authors.initials: D
authors.lastname: Danon
authors.forename: R
authors.initials: R
authors.lastname: Mashiach
authors.forename: I
authors.initials: I
authors.lastname: Meizner
authors.forename: A
authors.initials: A
authors.lastname: Ben-Haroush
mesh_terms: D000328:Adult; D001724:Birth Weight / Q000502:physiology; D002508:Cephalometry / Q000379:methods* / Q000592:standards; D005260:Female; D005865:Gestational Age; D006257:Head / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000196:embryology; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011237:Predictive Value of Tests; D011247:Pregnancy; D012015:Reference Standards; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal / Q000379:methods* / Q000592:standards