Evaluating the accuracy of sonographic fetal weight estimations using the Hadlock IV formula in a Chinese population

Despite being the most generalized formula in China, the Hadlock IV formula has never been examined to determine if it is suitable for Chinese newborns, nor have the factors that might affect its performance been investigated. However, previous studies have reported varying results about other formulas in other nationalities. This study sought to evaluate the performance of the Hadlock IV formula in estimating fetal weight (FW) in pregnant Chinese women and use ultrasound to identify the factors affecting the accuracy of estimations of newborn weight; through these means, we aimed to create a reference for predicting neonatal weight for obstetricians.

A retrospective observational study comprising data from 976 cases of live-birth singleton pregnancies at the Shanghai General Hospital was conducted. The participants' clinical data were examined and subjected to a logistic regression analysis to identify the multitude of possible factors affecting the estimation of FW. The proportions and correlations between the accurate and inaccurate estimation groups were compared to determine the different prognosis of these 2 groups. The correlations between the accuracy of the sonographic-based fetal weight estimation (SFWE) and newborns with different weight ranges were also analyzed.

The overall accuracy rate of the SFWE predicted by the Hadlock IV formula was 79.61%, while that of the inaccurate estimation group was only 20.39%. The incidence of spontaneous vaginal delivery (VD) was lower in the inaccurate estimation group than in the accurate estimation group (40.7% vs. 48.13%; P=0.041). In the inaccurate estimation group, 11.56% (23/199) of the participants underwent a secondary cesarean section (sCS), compared to only 6.44% (50/777) in the accurate estimation group. The low birth weight (LBW) rates and macrosomia rates were lower in the accurate estimation group than in the inaccurate estimation group, with odds ratios (ORs) of 0.483 and 0.459, respectively (P<0.05). The results indicated that the SFWE was more accurate for newborns weighing 2,500-4,000 g than those weight out of this range. In relation to macrosomia, the SFWE was likely to be underestimated, but it was usually overestimated in the LBW group.

The overall performance of the Hadlock IV formula in predicting the birth weight of Chinese newborns remains suboptimal. Extra caution should be exercised in cases of suspected large-for-gestational age (LGA) infants, small-for-gestational age (SGA) infants, infants with macrosomia, or LBW fetuses in the Chinese population.