An evaluation of two methods for measuring fetal head and body circumferences.

Abstract
Head and abdominal circumference measurements of 166 fetuses (15‐40 weeks) were made by three different examiners using two measurement techniques. In method 1 the actual circumferences were measured using an electronic digitizer, while in method 2 the circumference measurements were estimated using the formula for calculating the circumference for an ellipse. Evaluation of the entire data set as a whole demonstrated no significant mean errors (P > 0.05), and only a small degree of variability (2 SD = 6 per cent). Evaluation of the data for each examiner demonstrated no significant differences (P > 0.05) in the observed variability, but small statistically significant mean errors (1.7‐4.1 per cent) were observed. The latter finding is thought not to be a limitation of the ellipse approximation technique, since similar findings have been observed when experienced sonographers make actual circumference measurements on the same fetus using the same equipment.

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