The fetal cerebellar vermis: normal development as shown by transvaginal ultrasound.
OBJECTIVE: To determine the normal appearance and development of the fetal cerebellar vermis using mid-sagittal planes obtained by transvaginal sonography. SUBJECTS AND METHODS: A total of 101 fetuses were evaluated by transvaginal sonography between 21 and 39 weeks of gestation. The mid-sagittal antero-posterior and cranio-caudal vermian diameters, circumference and surface area were measured and calculated. Nomograms were produced. RESULTS: The vermis was observed in 96% of the cases and all the measurements were performed in 92%. The vermis grows in a linear fashion throughout pregnancy. The growth pattern correlates well with gestational age, biparietal diameter, head circumference and transverse cerebellar diameter. CONCLUSION: Transvaginal sonography is a valuable tool in the study of the fetal vermis during the second half of pregnancy. Knowledge of its normal appearance may help identify developmental anomalies and enable accurate prenatal counseling.