Transvaginal ultrasound assessment of corpus callosal length in the fetus: multicenter cross-sectional study

To produce reference ranges and Z-scores for corpus callosal (CC) length in the fetus, based on transvaginal three-dimensional (3D) ultrasound imaging.

This was a cross-sectional multicenter retrospective study based on 3D volume dataset acquisitions of the fetal CC between the 15^th and 37^th weeks of gestation. Only volume datasets acquired transvaginally through the anterior fontanelle were selected. After plane alignment on multiplanar imaging, the length of the CC was measured edge-to-edge on magnified images. Intra- and interobserver variability were assessed and the related intraclass correlation coefficients (ICC) calculated. Biometric charts to assess the reference values for fetal CC were obtained using the method proposed by Altman in 1993.

The 13 participating centers provided valid data for 2131 patients. Excellent agreement was observed for both intra- and interobserver analysis, with an ICC range of 0.98-1.00. A quadratic model was used for construction of the reference charts, modified with the insertion of cubic spline coefficients with a single knot at 18 gestational weeks, to recover an apparent lack of fit at lower gestational ages. Centile reference values and the corresponding Z-scores were produced for CC length between 15 and 37 gestational weeks.

This multicenter study presents growth charts for the fetal CC, addressing the critical methodological weaknesses of several previous studies. An even distribution of cases across all gestational weeks, robust statistical methodology and a standardized, high-resolution transvaginal neurosonographic technique represent key factors supporting the reliability of the biometric curves presented here. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.