The Most Accurate Way of Predicting Birth Weight in China: Zhuo’s Formula

Abstract

Background: Pregnancy body mass index (BMI) influences fetal weight, yet no studies focused on the comparison of formulas’ predictive accuracy after considering it. Objective: This study aimed to find out the most accurate formula for predicting birth weight, especially in different BMI pregnant women. Methods: It is a prospective observational study. Using a convenient sampling, the participants who met the criteria for inclusion were recruited in a tertiary hospital from January to March 2019. BMI was calculated according to the pregnant woman’s weight and height at the first obstetric visit. The estimated birth weights were predicted by five formulas based on participants’ uterine height and abdominal circumference of the last obstetric examination. The actual birth weight was scaled in the delivery room. The root mean square error (RMSE), empirical cumulative distribution map (ECDP) and Bland–Altman plot were used to determine the accuracy of the formulas in predicting birth weight. Results: A total of 1197 pregnant women were recruited. The RMSE, median value and difference of Zhuo’s formula in predicting the actual birth weight were the smallest (348.7), the closest to 0 (20.0) g, and the smallest (-0.141 ± 11.511) g, respectively. In subgroup analysis, the RMSE of Zhuo’s formula was the smallest in the low and normal BMI groups, and the difference of Zhuo’s formula by Bland- Altman plot was the smallest (only 0.729±10.440) g in the overweight and obese group. Conclusion: Zhuo’s formula for predicting birth weight has the highest accuracy in different BMI groups. Thus, it is worth recommending for clinical use.