PURPOSE: To assess the normal range of,cerebral ventricular atrial dia
meters during the second and third trimesters of pregnancy. MATERIALS
AND METHODS: The transverse diameter of the atrium of the lateral vent
ricle was prospectively measured in 739 consecutive antenatal ultrasou
nd examinations by positioning electronic calipers on the luminal marg
ins of the ventricular wall, perpendicular to the long axis of the ven
tricle. RESULTS: The mean ventricular atrial diameter for the combined
group of all 739 studies was 5.4 mm +/- 1.2 (standard deviation). The
transverse diameter of the ventricular atrium did not progressively i
ncrease with advancing gestational age. All fetuses younger than 17 me
nstrual weeks had ventricular atrial diameters less than 8 mm. Four fe
tuses had ventricular diameters of 10 mm br greater. CONCLUSION: A rea
sonable upper limit of normal for transverse atrial diameter for gesta
tional age of 25 weeks and above appears to be 10 mm. Prior to 25 week
s, diameters over 8 mm are unusual in the healthy fetus and signal the
need for a detailed evaluation of fetal anatomy.