stuDy oF accuracy oF commonly useDFetal Parameters For estimation oF gestational age

Abstract

Estimation of the gestational age by sonographic measurements of fetal parameters is usually done
by measuring mean sac diameter (MSD), Crown-rump length (CRL), biparietal diameter (BPD),
head circumference (HC), femoral length (FL) and abdominal circumference (AC) depending on the
trimester of pregnancy. This is a prospective study to see the correlation of different fetal param-eters in estimating the gestational age. A total of 71 normal women were taken and ultrasonogram
was done to take MSD and CRL in 1st
trimester and BPD, HC, FL and AC in 2
nd
and 3
rd
trimester.
Gestational age was calculated by MSD using Rempen normogram and Hadlock normograms were
used for the rest of fetal parameters. Gestational age by LMP was also calculated at the same time.
Correlation of different fetal parameters in estimating gestational age in different trimesters was
done by Pearson correlation. Pearson correlation showed that the CRL was the best fetal param-eter (correlation coefficient of 0.909) in the first trimester. The correlation of MSD and average
gestational age by MSD and CRL was with correlation coefficients of 0.778 and 0.888 respectively.
Thus the averaging of gestational age in 1st
trimester decreases the accuracy in the gestational age
estimation. Correlation of gestational age by BPD, HC, FL and AC and their average in 2
nd
trimes-ter showed that the best correlation was by AC and the least correlation by BPD in this study. It
is in contrary to other studies which could be due to chance finding or bias because of prospective
study. Pearson correlation calculated in 3
rd
trimester showed HC and FL were better parameters
than BPD and AC. Average gestational age by simple averaging of BPD, HC, FL and AC gives
more accurate estimation of gestational age in both 2nd
and 3
rd
trimester.

Key Words: Ultrasonogram, Fetal parameters, Gestational age.