Charts of Thai fetal biometries: 3. Femur length

A cross-sectional study was conducted in order to construct a new reference chart for Thai fetal femur length (FL). A total of 621 normal pregnant women between 12-41 weeks of gestation and their fetuses were enrolled. Measurements were made once at a randomly assigned gestational age specifically for the purpose of this study only. Femur length data were available in 608 measurements due to unfavorable fetal position in some cases. Linear regression technique was used to model separately the mean and standard deviation as functions of gestational age. Reference centiles were constructed from a combination of both models, assuming the data were normally distributed. A new reference centiles chart for FL is presented and compared with previously published data. While our derived centiles were clearly lower than those from Western studies, they were found comparable with those from a Thai study. This demonstrated the important effect of racial differences between populations on fetal biometries and elucidates the need to develop fetal biometries charts specifically for each region.