<div>Epidemiological studies suggest impaired fetal skeletal development has lifelong consequences for bone health. To examine the feasibility of using 3-dimensional ultrasound (3DUS) to investigate influences on fetal femur development, we obtained volume datasets of the uppermost fetal thigh at 19 and 34 weeks gestation in 517 women in a population-based survey of maternal nutrition. In addition to the standard measure of femur length, we derived femoral cross-sectional areas and volume from

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... he volume datasets. Coefficients of variation for intra-operator variability in femur length were 0.6% at 19 weeks and 0.4% at 34 weeks; corresponding coefficients of variation for distal femoral cross-sectional area were 4.4% at 19 weeks and 3.2% at 34 weeks, showing greater measurement variability with a more complex technique. Intra-operator variability for femur volume measurement triplets at 19 and 34 weeks was 3.4% and 1.7%, respectively. The coefficients of variation of replicate measurements were compared with the between-subjects variation as a measure of the biological variability between fetuses: at 19 weeks between-subjects variation was 7.2% for femur length, 19.6% for distal cross-sectional area and 19.9% for femur volume. These results show a wide range of variation between subjects, which is substantially greater than the intra-operator variability. This suggests that the measurements of fetal femur size and volume are reproducible and can be used to examine biological differences between subjects, and we found that femoral volume was greater in male fetuses at 19 weeks gestation. Thus 3DUS presents a useful technique for assessing fetal skeletal development in cohort studies</div><br />