Fetal lateral ventricular ratio determination during the second trimester.

Ventriculomegaly may be diagnosed sonographically by identifying abnormal ventricular size. The lateral ventricular ratio (LVR) is a useful index in differentiating normal-sized ventricles from ventriculomegaly. The purpose of this study was to validate previously reported data establishing the normal range for LVR during the second trimester. Prior to 24 weeks, the diagnosis of ventriculomegaly may be difficult since the LVR normal range is quite large. The LVRs for 122 normal fetal ultrasound examinations were calculated based on measurements obtained by three observers. Data were obtained for fetuses during each week of gestation from 15 to 25 weeks. Lateral ventricular ratios varied from 56 +/- 18 per cent (mean +/- 2 standard deviations) at 15 weeks to 33 +/- 4 per cent at 25 weeks. The lateral ventricular width (LVW) range for normal fetuses was 0.7 to 1.1 cm as compared with a LVW range of 1.1 to 2.7 cm for 16 fetuses with hydrocephalus diagnosed during the second trimester. In conclusion, the LVR is extremely useful in differentiating ventriculomegaly from normal ventricular size. Serial ultrasound examinations are often mandatory in the second trimester in order to definitely identify ventriculomegaly. In addition, normal ventricular size may be verified with a LVW of less than 1.1 cm.