Can the anterior–posterior thigh diameter be used as an indicator for fetal age using two-dimensional sonography?☆

Abstract 

This study evaluated the usefulness and direct correlation of a simple new method of predicting fetal age by measurement of the anterior–posterior thigh diameter (APTD) in a normal 18 to 28week pregnancies using two-dimensional sonography. Little published research exists in the area of fetal thigh biometry, specifically in the use of the anterior–posterior fetal thigh diameter (APTD). The only study I found was that of fetal thigh circumference. Continuing review of existing practices needs to be coupled with evaluation of alternate or additional methodology.

Materials and methods

This was a quantitative prospective study of 55 patients in High Level General Hospital, Alberta, Canada. Anterior–posterior thigh diameters (APTD) were sonographically measured. The normal range for each week of pregnancy was determined five times for reliability.

Results

Significant correlation was found between (APTD) and fetal age from simple line regression analysis, with 99.993% confidence intervals at each week from 18 to 28weeks gestation. There was a correlation of 1mm APTD per 1week of fetal age. In addition R>0.93, P<0.001. The residual scatter plots confirmed the APTD validity.

Conclusion

APTD is a reliable and valid method for assessing fetal age in a normal pregnancy and may be particularly useful when other parameters are unable to accurately predict fetal age. An accurate linear measurement of multiple fetal parameters allows a more complete profile of fetal growth and estimated date of delivery (EDD). APTD may also be useful in identifying fetal growth problems. All of the values of fetal age lie directly on the “best-fit” regression line. Since the coefficient of determination (Rsq) is very high, this model is very effective.

Keywords: Fetal age, APTD, Parameters