Development of the human fetal corpus callosum: a high-resolution, cross-sectional sonographic study.

OBJECTIVE To establish reference ranges during human pregnancy for normal fetal corpus callosum dimensions. DESIGN In a prospective, cross-sectional study of 258 fetuses between 16 and 37 weeks of gestation, measurements of the length, width, and thickness at the level of the anterior mid-body of the corpus callosum were performed, using high-resolution, transvaginal and transabdominal transducers. RESULTS The mean length of the corpus callosum was 27.2 (standard deviation, 1.2; 95% confidence interval, 26.02-28.37) mm. Width and thickness of the corpus callosum were 5.6 (standard deviation, 1.6; 95% confidence interval, 5.41-5.82) mm and 1.9 (standard deviation, 0.7; 95% confidence interval, 1.87-2.06) mm, respectively. The size of the corpus callosum as a function of gestational age was expressed by regression equations: length (mm) = -20.40 + 1.92 x gestational age; width (mm) = -0.052 + 0.225 x gestational age; thickness (mm) = -0.174 + 0.085 x gestational age. The dimension-gestational age correlation coefficients were: r = 0.779 for length, r = 0.676 for width and r = 0.494 for thickness; these were statistically significant (P < 0.01). The maximum increase in thickness and width of the corpus callosum occurred between 19 and 21 weeks' gestation, while its length followed a constant growth rate. The normal mean length, width and thickness of the corpus callosum per week, and the 95% confidence limits, were defined. CONCLUSIONS The present study offers normative measurements of the fetal corpus callosum and may facilitate a more objective diagnosis of its congenital abnormalities.