Circumference measurements in obstetrical ultrasound: ellipse vs. arithmetic mean.

Quantitation of fetal parameters by prenatal sonography enables the assessment of menstrual age and fetal development. Appropriate fetal growth can be surmised on the basis of sequential measurements, as well as the relative variation of parameters such as biparietal diameter (BPD), femur diaphysis length (FDL), abdominal circumference (AC 1, and head circumference (HC). Accurate determination of these quantities to within an acceptable range of measurement error is essential to ensure reproducibility of results and to document true growth patterns. Assuming images are acquired at appropriate anatomic levels, major sources of measurement error are related to