RESUMO
OBJECTIVE: To establish normal reference intervals for biparietal diameter, head circumference, abdominal circumference, and length of femur, a cross-sectional study. STUDY DESIGN: Five hundred singleton fetuses for each week at gestations between 23 and 41 weeks with a total of 9500 fetuses. Antenatal ultrasound measurements from all consecutive pregnant women referred to the ultrasound unit for scanning of fetal condition are prospectively entered in a data bank. For the purpose of this study, sonographic measurements were collected retrospectively and each fetus contributed just one value to the reference sample. RESULTS: The mean curve of the four biometrical parameters varied with gestational age, with flattening of the curves at the end of gestation and increased width of normal ranges with increasing gestational age. Maximal weekly increases occurred at 24 weeks' gestation for head circumference, abdominal circumference, and length of femur and at 26 weeks' gestation for biparietal diameter. The four biometrical parameters, however, showed 50% increases in size at 33 weeks' gestation. CONCLUSIONS: These fetal size reference intervals are clinically relevant and can be used for populations with epidemiological features and distribution of neonatal birth weights similar to our data.
