Sonar biparietal diameter. II. Predictive of three fetal growth patterns leading to a closer assessment of gestational age and neonatal weight.

Serial BPD readings were obtained from 142 normal parturients, with established dates, between 20 to 40 weeks of pregnancy. It is noted that fetal BPD's can be separated into one of three percentile rankings: large (i.e. above the seventy-fifth percentile), average (i.e. twenty-fifth to seventy-fifth percentile), and small (i.e. below the twenty-fifth percentile). In addition, it is shown that, under normal conditions, fetuses intially placed in any one of these cephalic levels will continue to grow within the confines of the same percentile range. This biologic phenomenon has not been previously reported in human fetal growth. It is important because it leads to a closer prediction of fetal age and a better assessment of neonatal weight and outcome.