In this study, the cardiac circumference as measured in a four-chamber view was analyzed to determine its relationship to three linear, sonar measurments—biparietal diameter, femoral length, and abdominal circumference—and two sonographically derived fetal parameters— gestational age and estimated fetal weight. The results showed that the magnitude of the cardiac circumference as a function of any or all of these variables be used as an index of organ size when assessing fetuses at risk for anomalous cardiac development.