Estimation of fetal weight at term by clinical and sonographic assessment and its correlation with the birth weight – A prospective cohort study in a tertiary care hospital

Estimation of fetal weight is necessary to decide on the time and route of delivery. Different clinical and ultrasound methods for estimating fetal weight are followed by different institutions. Antenatal assessment of fetal weight is necessary to achieve better feto-maternal outcomes. The objectives of this study were: (a) fetal weight estimation by ultrasound (Hadlock’s formula) and clinical methods (Johnson’s formula and Dare’s formula) and (b) to compare them with the actual weight of the baby after birth. A prospective cohort study was conducted in a tertiary care centre at Puducherry, India including all singleton, term pregnant women with vertex presentation, normal AFI and BMI <35 kg/m who delivered within the next 48 hours of assessment. The agreement between the different methods of fetal weight estimation and actual birth weight were calculated using intraclass correlation coefficient. Bland and Altman plot was done to identify the intervals of agreements. A total of 400 term antenatal women with age range of 17 to 44 years participated in the study. Intraclass correlation coefficient for Johnson’s formula was 0.816, Dare’s formula was 0.672 and Hadlock’s formula was 0.912. All the three methods had statistically significant correlation with the actual birth weight. Ultrasound estimation of fetal weight is the best out of the three methods and it correlated well with the actual birth weight. Johnson’s formula also gave results close to actual birth weight. With a correlation coefficient comparable to that of ultrasound estimation, Johnson’s formula can be used in low resource settings where ultrasound facilities are not available.