Abnormal fetal head circumference 2025-11-19T08:18:04Z Any deviation from the normal range of the fetal head circumference, which is typically measured sonographically in the axial plane at the level of the thalami and cavum septic pellucidi, using the outer border of the bony calvarium. Abnormal fetal head circumference is defined as less than the thrid percentile or 2 standard deviations below the mean or greater than the 97the percentile or 2 standard deviations above the mean. Fetal head anomaly