New formula for estimating fetal weight below 1000 g: comparison with existing formulas.

Abstract

Most estimated fetal weight formulas have been derived and tested with larger fetuses, yet accuracy in predicting birth weight is more critical at the limit of viability. Complete data from 142 pregnancies in which delivery took place within 7 days of an ultrasonographic examination were used to create an appropriate formula for fetuses less than 1000 g and compare it with 10 currently available formulas. Our formula (In [BW] = 0.66 x 1n [HC] + 1.04 x 1n [AC] + 0.985 x 1n [FL]) was significantly more accurate than all other formulas and also performed better on a prospective cohort of 27 fetuses with estimated fetal weight less than 1000 g. Of the existing formulas, the Hadlock formula (using head circumference, abdominal circumference, femur length) was the most accurate, being significantly more accurate than all but the Woo formula with all but the Woo formula.

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

“…This confirms results obtained by Medchill et al [20] in a retrospective series of 76 fetuses, and by Kaaij et al [21] who have reported the largest series so far of 100 infants with a birth weight !1,000 g. Only few authors have recommended the use of specifically targeted very-low-birth-weight infant formulas. For Pielet et al [22] and Scott et al [7] specific formulas targeting very-low-birth-weight infants gave a better accurate prediction of fetal weight. However, it should be underlined that the number of fetuses included in those series is small.…”

“…Pielet et al [22] studied only 30 fetuses. Scott et al [7] tested a new formula (created by using retrospective biometric data of 142 pregnancies of !1,000 g) in only 27 fetuses.…”

“…Biometric data on each of the 119 fetuses were used to evaluate the accuracy of ten published fetal weight formulas (table 1). The choice of these formulas was based on the following considerations: (A) the formulas of Campbell [14] and Shepard [2] were the first to be published and have been used as a reference in most studies relating to sonographic estimation of fetal weight; (B) the formulas of Rose [5], Hadlock [3] and Sabbagha [16] are those which, in our experience, show the best accuracy for fetuses born at term or close to term, and (C) the formulas of Weiner [6], Scott [7], Thurnau [8], Mielke [9] and Weinberger [10] were specifically developed for very premature and/or very-low-weight fetuses.…”

“…less relevant to very low birth weight infants. Therefore, some authors have sought to develop new formulas specifically adapted to highly premature and/or very-lowweight fetuses [6][7][8][9][10].…”

Waist Circumference as a Predictor of Failure of Sonographic Estimation of Fetal Birth Weight

“…Although conflicting results were reported when comparing with more recent models, the Hadlock formula was reported to be comparable and even better in EFW prediction in several publications [16,17,18]. In our study, we preferred the Hadlock model for sonographic EFW because of its wide acceptance and the available embedded software in our sonographic equipments.…”