Accurate  knowledge  of fetal  age  is  very  important .  A number of

   methods  can  be used to determine an accurate gestational age . With

   routin  use  of  ultrasonography  more  information about the anatomy of

   the  fetus  can  be  obtained . one of  the  parameter that can be used is

   biparietal diameter .

        This   study   was   carried  out in 386 pregnant women with known last

   menstrual period . Regression   analysis  was   performed  to evaluate the

   relationship  between biparietal diameter and menstrual age.

         Regression analysis indicated that menstrual age could be predicted

   with3.5 weeks with 95% interval confidence.This was also computed for

   three gestational  age  interval :  20-26  weeks ,  26 - 32  weeks and 32-42

   weeks.The results indicated that prediction   of  age become progressivly

   less accurate as pregnancy proceed .