Fetal Macrocephaly Diagnosis and Definition

Diagnostic Criteria

• Fetal macrocephaly is defined as a head circumference (HC) exceeding 2 standard deviations (SD) above the mean for gestational age, which corresponds to above the 97th-98th percentile, according to the American College of Obstetricians and Gynecologists 1, 2
• The primary diagnostic criterion is HC >2 SD above the mean (>97th percentile) for gestational age and sex, which represents the standard definition used in prenatal ultrasound assessment, as recommended by the American Institute of Ultrasound in Medicine 1
• Mild macrocephaly is defined as HC between 2 and 3 SD (between 97th and 99.7th percentile) above the mean, as defined by the International Society of Ultrasound in Obstetrics and Gynecology 1, 2

Measurement and Assessment

• Serial measurements are more valuable than single measurements for assessing growth trajectories and confirming the diagnosis, with a moderate level of evidence, as suggested by the American College of Radiology 3