A study to estimate the gestational age by measuring bi-parietal diameter of the foetuses in Gravid Females

Abstract

Introduction: Monitoring of intra-uterine growth has remained a very important fetal surveillance tool in the care of pregnant women. In wide variety of circumstances of feticide the fetal age determination is important for identification. There are many parameters to determine the age of the fetus during autopsy, which includes measurement of BPD and head circumference in the skull. if during autopsy of a decomposed or mutilated body only skull is present then BPD is useful criteria for estimating age. Biometric values or curves of one population may overestimate or underestimate the fetal age if used for other population with different demographic characteristics. Therefore, this study was undertaken to assess GA with the help of measurement of BPD by ultrasonography. Methods: This Prospective Cross Sectional study involved Prior Consent & was found to be within ethical standards. Study was carried out to measure BPD of the fetus in a total of 100 gravid females by using a grey scale real time Sonography Machine employing a 6-3 MHz convex transducer.The fetal head was imaged in an axial section with the fetus in direct occiput transverse position. The instrument was set so that parietal bones measure approximately 3 mm in thickness. The BPD was measured from the outer surface of skull table to the inner margin of the opposite skull table in a transverse plane.Results: The study was conducted among 100 Gravid Females. Cubic polynomial regression model was fitted to measure BPD as a function of GA. The models were chosen based on the correlation coefficient, R2 To illustrate the variability in measurement, the Standard Deviations of each week were computed and regressed on GA using a simple linear equation. In this study, fetal mean BPD showed linear increase from 13 to 36 weeks and statistically significant correlation was found between GA and BPD. Average growth rate of BPD was found to be 0.31 cm/week from 13 to 28 weeks. Conclusions: This study substantiates the fact that BPD is one of the useful criteria to predict GA and determine EDD and it was found to be statistically significant. We have been able to generate growth charts and an equation for monitoring growth and estimating GA based on a large sample in an area where many mothers are unsure of the date of their last menses and might be at risk of intra-uterine growth restriction. This we believe will guide antenatal caregivers from under-estimation or over-estimation of GA. Accuracy in measurement and resolution in these parameters are of immense importance.