Sex-specific fetal weight prediction by ultrasound

Objective: To improve sonographic birth-weight prediction by developing fetal gender-specific formulae.

Methods: This was a retrospective cross-sectional study. Two gender-specific formulae were produced from the data of 527 patients and the data of a further 349 patients were used to evaluate the formulae. Inclusion criteria were a singleton live fetus, gestational age above 25 weeks, birth weight between 1000 g and 4500 g and fetal biometry within 8 days of delivery. Data retrieval was specifically for the purpose of this study.

Results: To yield the best-fit weight formula for each fetal gender we employed step-wise regression analysis based on fractional polynomials with the biometric parameters biparietal diameter (BPD), head circumference (HC), transverse abdominal diameter (TAD), abdominal circumference (AC) and femur length (FL): estimated fetal weight for girls (g) = - 4035.275 + 1.143 x BPD3 + 1159.878 x AC1/2 + 10.079 x FL3 - 81.277 x FL2 [in cm]; estimated fetal weight for boys (g) = 43576.579 + 1913.853 x log10BPD + 0.01323 x HC3 + 55.532 x AC2 - 13602.664 x AC1/2 - 0.721 x AC3 + 2.31 x FL3 [in cm]. These formulae showed superior results compared with those of conventional weight formulae.

Conclusion: Gender-related fetal weight calculation allows optimized prediction of fetal weight at birth.