RESUMEN
The utilization of a specific approximation or equation derived from a specific ethnic population is a reasonable approach to the estimation of gestational age for such a population with more reliability and confidence. The biparietal diameter of an Egyptian population was studied over the gestational period of 10 to 42 weeks. A stepwise regression model for BPD growth was derived with a high degree of correlation with the gestatioal age [R-squarred is 0.9896]. The equation which extrapolate the mean gestional age and 95 confidence limit for this population on the basis of BPD is Gestational week = 8.30911 + [0.19318*BPD] + [0.00075* BPD [2]] + [4.583944 E-10*BPD [5]]. The standard error of estimate is 0.94 weeks [6 days] all over the period of estimation support the high percision of the equation for in-utro fetal age assessment