The corpus callosum: Normal fetal development as shown by transvaginal sonography

OBJECTIVE. Detection of the corpus callosum in the developing fetus on sonograms usually is difficult. We determined the normal appearance and development of this structure during the second half of pregnancy, as shown on transvaginal sonograms. SUBJECTS AND METHODS. One hundred one fetuses were evaluated with transvaginal sonography between 18 and 42 weeks' gestation. The length of the corpus callosum and the thicknesses of the genu, body, and splenium were measured, and growth tables were produced. RESULTS. The corpus callosum was detected in 95% of cases and showed gradual enlargement during pregnancy; growth was linear, from nearly 17 mm in length at 18 weeks' gestation to 44 mm at term. The ratios of the length of the corpus callosum to the anteroposterior diameter of the brain remained relatively constant from 20 to 21 weeks' gestation to term. CONCLUSION. Transvaginal sonography can be used to visualize and measure the corpus callosum in the developing fetus. Data from this study may be useful as a reference for normal development of the corpus callosum.