A new formula for calculating weight in the fetus of 1600 g

Authors: R. L. Schild¹; K. Fell¹; R. Fimmers²; U. Gembruch¹; M. Hansmann¹

Source: Ultrasound in Obstetrics and Gynecology, Volume 24, Number 7, December 2004 , pp. 775-780(6)

Publisher: John Wiley & Sons, Ltd.

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Abstract:

Objective

To develop and test a new formula for estimating weight in the fetus of

1600 g.

Methods

A formula for sonographic estimation of fetal weight was produced retrospectively from 84 singleton fetuses with a birth weight of

1600 g, examined sonographically within 1 week before delivery. Exclusion criteria were multiple pregnancy, intrauterine death and major structural or chromosomal anomalies. The new formula was then compared prospectively in an evaluation group of fetuses (n = 87) with six currently available equations for estimating weight in the preterm fetus.

Results

Stepwise regression analysis with gestational age (in days) and fetal biometric parameters was employed to yield the best-fit formula for predicting fetal weight at birth. The new formula (estimated fetal weight = 5381.193 + 150.324 × head circumference + 2.069 × femur length³ + 0.0232 × abdo- minal circumference³—6235.478 × log(head circumference)) proved to be superior to established equations. The lowest mean ± SD absolute error was 66.2 ± 59 g and the lowest mean absolute percentage error was 7.1 ± 5.9% SD when studied prospectively in the evaluation group. With the new formula, 48.3% of estimates fell within ±5% of the actual weight at birth, 73.6% fell within ±10%, 90.8% fell within ±15% and 95.4% fell within ±20%.

Conclusion

Our new formula is relatively easy to use and needs no adjustment to weight centiles or to fetal lie. It allows reliable weight estimation in the fetus

Keywords: fetal weight; small fetus; ultrasound

Document Type: Research article

DOI: http://dx.doi.org/10.1002/uog.1741

Affiliations: 1: Department of Obstetrics and Fetal Medicine, Centre for Obstetrics and Gynaecology, Germany 2: Institute for Medical Statistics, University Hospital Bonn, Germany

Publication date: 2004-12-01

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A new formula for calculating weight in the fetus of 1600 g

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