A Comparative Study of Estimation of Fetal Weight in Term Pregnancy by USG and Clinical Methods with Actual Birth Weight in Tertiary Care Center

Background: The ability to estimate fetal weight at term is important for good obstetric management, as low birth weight and macrosomia are linked to maternal and neonatal morbidity. Clinical methods (Johnson's formula) and ultrasonographic methods (Hadlock's formula) are widely used, but the comparative accuracy is different in different populations. The objective is to examine the accuracy of clinical estimation (Johnson's formula) of fetal weight in comparison to ultrasonographic estimation (Hadlock's formula) of fetal weight in comparison to actual birth weight, and to examine the correlation between both methods Material and Methods: The study is a prospective comparative study done on 100 primigravida women with singleton term pregnancy (37-42 wks) with vertex presentation in the hospital setting. Fetal weight was estimated clinically using Johnson's formula using symphysio-fundal height and fetal station. The ultrasonographic estimation was performed within 7 days before delivery by Hadlock's formula with fetal biometric parameters (BPD, HC, AC, FL). The actual birth weight was measured and taken as the gold standard immediately after delivery. Pearson correlation and percentage error assessment were used for statistical analysis. Results: The mean actual birth weight was 2880.96 ± 416.89 g. The mean value in clinical estimation was higher (3019.81 ± 376.18 g), suggesting a trend towards overestimation while the ultrasonographic estimation (2880.8 ± 341.74 g) was closer to the actual birth weight. The ultrasonography was more accurate with 74% within 10% of the estimate versus 68% for clinical estimation. The percentage of estimates >20% was significantly lower with ultrasonography (2% vs. 8%). Both methods were well correlated with actual birth weight with ultrasonography showing a higher r value (r = 0.819) than clinical estimation (r = 0.761); both of these were significant (p < 0.0001). Conclusion: The ultrasonographic estimation by Hadlock's formula is more accurate and reliable than the clinical estimation by Johnson's formula. However, clinical techniques are useful and important, especially in low resource areas, and can be useful adjuncts in fetal weight assessment.

Keywords: Fetal weight estimation, Johnson’s formula, Hadlock formula, ultrasonography, birth weight.