Sonographic estimation of fetal head circumference: How accurate are we?

N. Melamed, Y. Yogev, D. Danon, R. Mashiach, I. Meizner, A. Ben-Haroush

Research output: Contribution to journalArticlepeer-review


Objectives 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 > 90th 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. Conclusion 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.

Original languageEnglish
Pages (from-to)65-71
Number of pages7
JournalUltrasound in Obstetrics and Gynecology
Issue number1
StatePublished - Jan 2011


  • accuracy
  • error
  • head circumference
  • postnatal
  • random error
  • sonographic
  • systematic error


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