Publication:

Comparison of ultrasound scan fetal weight estimation and the combination of Dare and Johnson fetal weight estimation

Background Accurate estimation of fetal weight in pregnancy is key in decision making and determining when, where and how a delivery will occur, thereby contributing to the reduction of adverse pregnancy outcomes. Clinical and imaging methods have some degree of inaccuracy in estimating the fetal weight. This study aimed to evaluate the accuracy of fetal weight estimation by combination of the Dare and Johnson formulae compared with the Hadlock 2 ultrasound method in term pregnancies.

Methods The study was a comparative cross-sectional study of 144 randomly selected pregnant women at the department of obstetrics and gynecology of the University of Port Harcourt Teaching Hospital from 1st June to 30th November, 2024. The degree of accuracy of fetal weight estimation using a combination of Dare and the Johnson formula and the Hadlock 2 ultrasound method was calculated using the mean absolute error, mean absolute percentage error, and the proportion of estimates within 10% of actual weight.

Results The combination of the Dare and Johnson formulae overestimated fetal weight by 859.15±418.23 gm with a mean absolute percentage error of 25.13±15.18%. In comparison, the Hadlock 2 ultrasound scan method, underestimated the fetal weight by 163.01±253.19 gm with a lower mean absolute percentage error of 4.45±7.27%. The proportion of the combination of the Dare and the Johnson formulae, which is within 10% of the actual weight, was only 6.94%, while that of the Hadlock 2 ultrasound scan method had 76.39%.

Conclusions The Hadlock 2 ultrasound scan method of fetal weight estimation has higher accuracy and should be preferred approach when available. However, in low-resource settings where ultrasound technology may not be available, the combination of the Dare and the Johnson formulae may be used, but with caution since it is less accurate.