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

Abstract

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

Methods: 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.

Results: 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.

Conclusions: 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.

Keywords: biometry; corpus callosum; fetus; neurosonography; three‐dimensional ultrasound.

Figure 1

Multiplanar display of fetal corpus callosum (CC) at 22 + 3 weeks' gestation, from a three‐dimensional volume dataset acquired transvaginally, with volume contrast imaging (1‐mm slice). Maximum CC length was measured in the midsagittal plane (plane A) with calipers positioned on‐to‐on (edge‐to‐edge). Plane B is coronal plane and plane C is axial plane.

Figure 2

Histogram showing number of patients with transvaginal ultrasound three‐dimensional neurosonographic volume datasets used to measure fetal corpus callosal length at each gestational week. Total number of cases: 2131; number of cases per week ranged from 49 to 140.

Figure 3

Biometric curve of fetal corpus callosal (CC) length, measured on native two‐dimensional ultrasound images from three‐dimensional multiplanar imaging datasets, without volume contrast imaging, plotted against gestational age. 2.5^th, 5^th, 50^th, 95^th and 97.5^th centile curves are shown. Related percentages of cases above 97.5^th and 95^th centiles and below 5^th and 2.5^th centiles are shown for five gestational‐age classes.

Figure 4

Fitted values of cubic spline regression model for corpus callosal (CC) length, measured on native two‐dimensional ultrasound images from three‐dimensional multiplanar imaging datasets, without volume contrast imaging, plotted against gestational age, with corresponding estimates of CC length according to gestational age reported by studies included in the systematic review by Corroenne et al.. Only first author of each study is given. One implausible value in the data of Malinger and Zakut, probably due to a typo, has been corrected.