Ultrasonic measurement of the fetal ventricular system.

The ventricular systems of 178 fetal heads, ranging from 13 weeks gestation to term, were examined with ultrasonic "B" scans. The width of the frontal horns and of the third ventricle was measured. The distances between the temporal horns and between the sylvian fissures were also examined. The most important clinical measurement is that of the frontal horns. The combined width of the two frontal horns averaged 1.1 cm at 13 weeks and grew to an average of 2.4 cm at term. The 99% upper limits of confidence for these measurements were 1.45 cm and 2.78 cm, respectively. The frontal horn to BPD ratio decreased from 0.48 at 13 weeks to 0.25 at term. These measurements are considered important for the evaluation of possible ventricular dilatation in utero.