Validity of Sonographic Formulas for Estimating Fetal Weight below 1,250 g: A Series of 119 Cases

Abstract

Objective: The aim of this study was to determine the accuracy of sonographic methods for estimating fetal weight <1,250 g on the basis of ten published formulas falling into two principal categories: general formulas applied to all fetuses, and formulas specifically developed for very-low-weight fetuses. Methods: Recent biometric data (obtained less than 7 days before birth) on 119 fetuses weighing <1,250 g were used retrospectively. Estimated fetal weights derived from ten published formulas were compared to actual weights. For each equation, the errors in predicting fetal weight were used to calculate mean percentage error and standard deviation of the mean error. The t test was used to determine whether the mean errors were significatively different from zero. The F test was used to determine if there were significant differences in the standard deviation of the mean errors. Results: The mean birth weight of infants was 956 ± (SD) 183 g at a gestational age of 29 ± (SD) 2.3 weeks. The best three formulas were the Hadlock, Sabbagha and Mielke which generated a mean error of –0.25, 2.81 and 0.29 not statistically different from zero with standard deviations of 13.02, 9.14 and 11.96, which were not statistically different. Conclusion: In our population of very-low-birth-weight infants, the use of specific formulas targeted to those fetuses does not provide a more accurate estimation of fetal weight.

Factors Influencing the Accuracy of Fetal Weight Estimation with a Focus on Preterm Birth at the Limit of Viability: A Systematic Literature Review

“…Seventeen studies tried to evaluate the best formula for FWE [6,7,9,11,12,13,14,15,16,17,18,19,20,21,22,23,24] (table 4). The most frequently examined formulas are those of Hadlock, which were compared to other formulas in all studies listed above, except in the study by Mills et al [9] who only compared two formulas (Shepard and Warsof).…”

“…The formulas of Campbell, Merz, Shepard and Warsof have been examined 7, 8, 12 and 8 times, respectively. Thirteen of the studies found one of the Hadlock formulas to be the most accurate [6,7,11,13,14,15,16,19,20,21,22,23,24]. All Hadlock formulas seem to be equally accurate, as Meyer et al [12] who compared five Hadlock formulas found no significant difference in systematic or random error.…”

“…Jouannic et al [23] reported that in addition to the Hadlock IV formula, the Mielke I formula achieved good results with mean errors not significantly different from zero either. This formula has only been examined twice but both studies considered it to be one of the most or the most accurate formula for VLBW fetuses [16,23]. In summary, the formulas of Hadlock seem to be the most accurate formulas for FWE in all BW ranges.…”

“…Of the 29 studies included, only five did not exclude multiple pregnancy [8,11,22,23,24]. Three examined the possible effect of multiple pregnancy on FWE [8,22,30].…”

Prediction of Small for Gestational Age: Accuracy of Different Sonographic Fetal Weight Estimation Formulas

“…While Barel et al [27] included EFW evaluations taken within 1 week of delivery, our study focused on EFW evaluations taken within 3 days of delivery, and in our cohort, most sonographic evaluations were performed even in a shorter interval; thus, it may minimize the error attributed to fetal growth within 1 week [28]. Other studies demonstrated a range of systematic error of 7-10% [29], 9-15% [30], 0-27.9% [5] and 8.5-37.6% [31]. However, this comparison is arguable due to methodological limitations attributed to relatively small sample sizes, differences in time interval from sonographic evaluation to delivery and different study populations (e.g.…”