Macrosomia: a new formula for optimized fetal weight estimation.
OBJECTIVE
To develop and test a specific formula for estimating weight in the macrosomic fetus.


METHODS
Ultrasound estimations of fetal weight were carried out within 1 week of delivery in 424 singleton fetuses with a birth weight of > or = 4000 g. Exclusion criteria were multiple pregnancy, intrauterine death and major structural or chromosomal anomalies. Stepwise regression modeling was used to derive a prediction formula with birth weight as the dependent variable and maternal booking weight and fetal biometric measurements as independent parameters. After a new formula for estimated fetal weight (EFW) had been developed in a formula-finding group (n = 284), it was compared with commonly used weight equations (evaluation group, n = 140).


RESULTS
The new formula (log(e)EFW = 7.6377445039 + 0.0002951035 x maternal weight + 0.0003949464 x head circumference + 0.0005241529 x abdominal circumference + 0.0048698624 x femur length) proved to be superior to established equations, with the smallest mean error (mean +/- SD, -10 +/- 202 g), the smallest mean percentage error (mean +/- SD, -0.03 +/- 4.6%) and the lowest mean absolute percentage error (3.69 (range, 0.05-13.57)%) when studied in the evaluation group. With the new formula, 77.9% of estimates fell within +/- 5% of the actual weight at birth, 97.1% within +/- 10%, and 100% within +/- 15% and +/- 20%.


CONCLUSIONS
The new formula allows better weight estimation in the macrosomic fetus.
Hart
N C
NC
Department of Obstetrics and Gynecology, Diakonische Dienste Henriettenstiftung, Hannover, Germany.
Hilbert
A
A
Meurer
B
B
Schrauder
M
M
Schmid
M
M
Siemer
J
J
Voigt
M
M
Schild
R L
RL
D000465:Algorithms; D001699:Biometry / Q000379:methods; D001724:Birth Weight / Q000502:physiology*; D005260:Female; D005320:Fetal Macrosomia / Q000000981:diagnostic imaging*; D020567:Fetal Weight / Q000502:physiology*; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011237:Predictive Value of Tests; D011247:Pregnancy; D012016:Reference Values; D016216:Ultrasonography, Prenatal / Q000379:methods