Age-related reference ranges for fetal foot length

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 r atio, based on a mathematical growth model. Method: In a prospective cross- sectional study of 610 pregnancies with sonographically confirmed gestation al age (<12 weeks' gestation), fetal biometry was performed in addition to measurements of fetal foot length between 12 and 42 completed weeks of gest ation. Reference ranges for the fetal foot and for the femur/foot length ra tio were constructed with an overall coverage of 90% of the measured data, using a previously established method of determining reference bands for gr owth parameters. Results: Foot length was noted to level off slightly up to 24 weeks of gestation and it continued in a nearly linear fashion thereaft er. The femur/foot length ratio was associated with a mean Value of approxi mately 7 up to 24 weeks of gestation, falling to below 1 after this time po int to a value of 0.85 at 41 weeks gestation. The comparison of the referen ce ranges established in this study with anatomic and sonographic reference ranges for the fetal foot demonstrates good conformity with the anatomic r eference range published by Streeter as early as 1920, and a large degree o f conformity with the sonographic reference range developed by Mercer and c o-workers. Conclusion: The proposed statistical approach offers reliable re ference ranges for the fetal foot and for the femur/foot-ratio as well.