Establishment of Reference Tables for Fetal Abdominal Circumference by Ultrasonographic Measurements in Local Population, Karnataka, India

Fetal Abdominal circumference (AC) is an important and most reliable individual parameter, which can be used not only for determining fetal age, fetal growth and the type of growth restriction.

1) To establish a reference table for fetal AC in normal pregnant women from 20 to 38 weeks of gestation from local population 2) To find out the predictive accuracy of GA(Gestational Age) determined by fetal AC with that determined by last menstrual period (LMP) method.

The data was collected by using predesigned pretested questionnaire from September 2016 to January 2018. Total 768 singleton pregnant women with minimum 30 cases for each gestational week from 20 to 38 weeks of gestation, fulfilling inclusion and exclusion criteria were studied.

The data was analyzed using Statistical Package for Social Sciences (SPSS) version 20. Percentages, mean, standard deviation and range, standard error, percentiles and regression equation etc. were performed for AC for each gestational week.

The regression equation derived was GA = 4.677 + (1.007 X AC in cm) with correlation coefficient (r) of 0.979 and proportion of variation in dependent variable (R²) of 0.959. by this regression equation, the accuracy in prediction of GA by AC measurements was ranging from 99.75% at 32 weeks to 94.61% at 38 weeks of gestation. The mean AC values of Hadlock's study were greater than that of the present study except at 20 weeks.

The present study findings confirmed that generation of population specific reference tables and regression equations for various fetal biometric parameters by a large scale study at national level is required for more precise reporting of GA and expected date of delivery (EDD) by ultrasonography.