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.