Comparative Performance of Ultrasonographic Fetal Biometry and Three Clinical Equations in the Intrapartum Period for Estimating Fetal Weight in Thai Singleton Pregnant Women Giving Birth at a Referral Tertiary Hospital

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Nuntapong Pongtipakorn
Pongsun Puntachai
Parinya Chamnan


Objectives: To compare the accuracy of fetal weight estimation by ultrasonography and three clinical equations and also to examine the ability of these estimation methods to predict low birth weight and macrosomia in Thai pregnant women giving birth at a referral tertiary hospital in northeastern Thailand.
Materials and Methods: Two hundred singleton pregnant women giving birth at Sanpasitthiprasong Hospital during September 2018 – March 2019 were recruited. Fetal weight was estimated by trans-abdominal ultrasound and three existing clinical equations: Dare’s, Johnson’s and Buchmann’s methods. Proportions of within 10% accuracy compared to actual birth weight were computed and measures of ability to predict low, normal birth weight and macrosomia (sensitivity/specificity, positive/negative predictive values and area under the receiver operating characteristics (AUR)) were compared using McNemar’s test and nonparametric method.
Results: The mean actual birth weight was 3,069.9 ± 464.8 grams. Overall, ultrasonography resulted in a higher proportion of within-10% accuracy than Dare’s, Johnson’s and Buchmann’s methods (70.5%, 38.5%, 24.5% and 58.5%, respectively, p < 0.001). Similar findings were observed for normal birth weight and for both term and preterm neonates. Ultrasonography had the best ability to predict low birth weight with sensitivity, specificity and AUR of 75% (95% confidence interval (CI) 51-91%), 94% (95%CI 89-97%) and 0.84 (95%CI 0.75-0.94), while Dare’s and Johnson’s methods better predicted macrosomia than the other two methods (p = 0.002).
Conclusion: Intrapartum ultrasonography had the highest accuracy in estimating actual birth weight, overall and particularly best in low birth weight. However, Dare’s and Johnson’s clinical equations appeared to predict macrosomia well and might probably be useful when large fetus is suspected in clinical practice.


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