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RESEARCH PRODUCT

Age-Related Reference Ranges for Fetal Foot Length

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AIM The aim of this study was to establish age-dependent reference ranges for fetal foot length with gestation as well as for the femur/foot length ratio, based on a mathematical growth model. METHOD In a prospective cross-sectional study of 610 pregnancies with sonographically confirmed gestational age (< 12 weeks' gestation), fetal biometry was performed in addition to measurements of fetal foot length between 12 and 42 completed weeks of gestation. Reference ranges for the fetal foot and for the femur/foot length ratio were constructed with an overall coverage of 90% of the measured data, using a previously established method of determining reference bands for growth parameters. RESULTS Foot length was noted to level off slightly up to 24 weeks of gestation and it continued in a nearly linear fashion thereafter. The femur/foot length ratio was associated with a mean value of approximately 1 up to 24 weeks of gestation, falling to below 1 after this time point to a value of 0.85 at 41 weeks' gestation. The comparison of the reference ranges established in this study with anatomic and sonographic reference ranges for the fetal foot demonstrates good conformity with the anatomic reference range published by Streeter as early as 1920, and a large degree of conformity with the sonographic reference range developed by Mercer and co-workers. CONCLUSION The proposed statistical approach offers reliable reference ranges for the fetal foot and for the femur/foot-ratio as well.