Increased accuracy of fetal weight estimation with a gender-specific weight formula.

OBJECTIVE To test whether Schild's sex-specific formula for estimating fetal weight is more accurate than commonly used regression formulae. METHODS The gender-specific formula and 10 widely used equations were evaluated in a group of 989 pregnancies. Each fetus underwent ultrasound examination with complete biometric parameters within 7 days before delivery. RESULTS Over the whole weight range and in the subgroup of newborns with a birth weight between 2,500 and 3,999 g, the sex-specific weight formula from Schild demonstrated the best level of accuracy. For infants with a birth weight of less than 2,500 g as well as for macrosomic newborns, the gender-specific formula did not improve fetal weight estimation. CONCLUSION In pregnancies where fetal gender is known, Schild's regression formula should be used when fetal weight lies within the range of 2,500-3,999 g.