Comparison of the Accuracy of INTERGROWTH-21 and Hadlock Ultrasound Formulae for Fetal Weight Prediction.

OBJECTIVE

To compare the accuracy of INTERGROWTH-21 (IG-21) versus Hadlock1 formulae for birth weight prediction on third-trimester ultrasound in a North American population.

METHODS

This single-centre retrospective cohort study included all pregnant patients who had a third-trimester ultrasound between 34 and 36 weeks gestation and delivered a term singleton at our maternal-fetal medicine reference centre between April 1 and July 30, 2019. Estimated ultrasound fetal weight was calculated with both Hadlock1 and IG-21 formulae for each fetus, then reported on a centile curve to adjust for gestational age at delivery, and compared with the actual birth weight.

RESULTS

The cohort included 600 women. The IG-21 formula had a comparable accuracy to Hadlock1 with mean absolute percentage errors (MAPEs) of 8.64 and 8.86, respectively (P = 0.191). Success rate, defined by a <10% discrepancy range of the actual birth weight, was significantly higher for IG-21 than for Hadlock1 (67.5% vs. 64.3%; P = 0.044).

CONCLUSION

Our results do not support the superiority of IG-21 to Hadlock1. There is a need for continued research to improve birth weight prediction with the ultimate objective of increasing the detection of small for gestation age and macrosomic fetuses.