Objective To construct new size charts for fetal head circumference, biparietal diameter and other head dimensions. Design A prospective, cross sectional study. Setting The routine ultrasound department of a London teaching hospital. Subjects The fetuses of 663 women seen in the routine antenatal booking clinic whose ultrasound and menstrual dates agreed within 10 days. Methods Fetuses were scanned once only for the purpose of the study at gestations between 12 and 42 weeks, when up to 20 dimensions were measured. For each measurement separate regression models were fitted to estimate the mean and standard deviation at each gestational age. Centiles were derived by combining these two regression models, assuming that the measurements have a normal distribution at each gestational age. Results A total of 594 fetuses had their biparietal diameter measured and their head circumference measured directly. Both head diameters were recorded for 587 fetuses and the circumference was also derived from these, as was the cephalic area. New charts are presented for biparietal diameter (both outer–outer and outer–inner), head circumference (directly measured and derived from diameters). The directly measured head circumferences were consistently (by about 1%) greater than those derived from measurement of the head diameters. The new charts are compared with previously published charts that are in wide use. Charts for occipitofrontal diameter, cephalic index and cephalic area are also presented. Conclusions We have constructed new size charts for the fetal biparietal diameter and for head circumference, both measured directly and derived from head diameters. We have demonstrated the difference between the size charts constructed from these two sets of values and hence the importance of using the appropriately derived chart when assessing the head circumference. The differences between the new charts for biparietal diameter and head circumference and previous ones may be largely due to methodological differences.

Identification of fetal growth retardation : comparison of Doppler waveform indices and serial ultrasound measurements of abdominal circumference and fetal weight. Obstet Gynecol 82, 23C236.

Objective To construct a new size chart for fetal femur length. Design A prospective, cross sectional study of fetuses scanned once only for the purpose of the study at gestations between 12 and 42 weeks. Setting The routine ultrasound department of a London teaching hospital. Subject The fetuses of 663 women seen in the routine antenatal booking clinic whose ultrasound and menstrual dates agreed within 10 days. Results Femur length was measured on 649 of the 663 fetuses. A linear‐cubic regression model was fitted to estimate the mean and a separate linear regression to estimate the standard deviation. Gentiles were derived by combining these two regression models, assuming that the measurements have a normal distribution at each gestational age. A new chart for femur size is presented and compared with previously published data. Conclusions We have constructed a new size chart for fetal femur length taking into consideration the increasing variability with increasing gestational age. We have compared our chart with other published data, and believe that the differences seen may be largely due to methodological differences.