Three-dimensional sonographic measurement of normal fetal brain volume during the second half of pregnancy.

OBJECTIVES This study was undertaken to develop a three-dimensional (3D) ultrasound method of measuring fetal brain volume. STUDY DESIGN Serial 3D sonographic measurements of fetal brain volume were made in 68 normal singleton pregnancies at 18 to 34 weeks of gestation. A comparison was made with fetal brain volume estimates from two-dimensional (2D) sonographic measurement of head circumference and published postmortem fetal brain weights. RESULTS Coefficient of variation for fetal brain volume (3D) caused by differences between repeated tests was 10.2% and between analyses of the same recorded volume 2.2%. Median brain volume increases from 34 mL at 18 weeks to 316 mL at 34 weeks. Median brain weight represented approximately 15% of total fetal weight. The 3D ultrasound-derived brain weight is larger than postmortem brain weight. However, this is not so for brain weight derived from total fetal weight at autopsy. A good agreement between 3D and 2D brain volume was found. CONCLUSION Sonographic measurement of fetal brain volume demonstrated an acceptable intraobserver variability and a nearly 10-fold increase during the second half of gestation.