Establishing Gestational Age-Specific Nomograms for Fetal Corpus Callosum Length: A Comparative Study of Two- and Three-Dimensional Ultrasonography

This study aims to establish gestational age and sex-specific nomograms for fetal corpus callosum (CC) length measured by two-dimensional (2D) and three-dimensional (3D) ultrasonography, and to evaluate measurement differences between these imaging techniques during the second trimester. The retrospective single-center study included singleton pregnancies that underwent detailed second-trimester ultrasonography between 19 and 25 gestational weeks. Fetal CC length was measured on the midsagittal plane using both 2D and 3D ultrasonography. Measurements were performed independently by 2 experienced perinatologists. Gestational age–specific percentile values (5th, 25th, 50th, 75th, and 95th) were generated separately for each modality. Agreement between observers and between imaging techniques was assessed using intraclass correlation coefficients. A total of 211 fetuses were included. Fetal CC length showed a progressive increase with advancing gestational age in both imaging modalities. No significant differences were observed between male and female fetuses. Measurements obtained by 3D ultrasonography were consistently higher than those obtained by 2D ultrasonography, with the difference reaching statistical significance. İn conclusion, the present study provides modality-specific nomograms for fetal CC length during mid-gestation and demonstrates that 3D ultrasonography yields higher CC measurements compared with 2D imaging. These findings support the use of separate reference ranges for each modality and suggest that 3D ultrasonography may offer practical advantages in the assessment of fetal midline brain structures.