Prediction of large for gestational age by various sonographic fetal weight estimation formulas-which should we use?

OBJECTIVE

As sonographic estimation of fetal weight (EFW) carries substantial impact, especially in large-for-gestational-age (LGA) neonates, we aimed to compare the accuracy of various formulas for prediction of LGA neonates.

STUDY

DESIGN

Retrospective cohort study of singleton gestations at term, with EFW up to 7 days before delivery (2007 to 2014). Small-for-gestational-age neonates were excluded. LGA prediction for various formulas was evaluated by: (i) measures of performance (sensitivity, specificity, etc.); (ii) systematic and random errors (SE and RE) and the proportion of estimates (POEs) exceeding 10% of actual birth weight. Best performing formula was defined as the one with the lowest Euclidean distance [=square root of (SE2+RE2)].

RESULTS

Out of 62 102 deliveries, 7996 met inclusion criteria, of which 1618 neonates were LGA (22%). There was a considerable variation in sensitivity (74.6±16.3%, 23.5% to 99%), specificity (86.3±10.6%, 51.7% to 99.6%), positive predictive value (64.9±12.4%, 35.6% to 93.8%), positive likelihood ratio (LR; 9.3±10.9, 2.1 to 54.2) and negative LR (0.3±0.16, 0.02 to 0.8), a mild variation in the negative predictive value (92.9±3.7%, 82.3% to 99.5%) and a minimal variation in the area under the curve (94.3%, 93.0 to 95.1; mean±s.d., range for all). Absolute SE was higher for the LGA group in 11/20 formulas (55%). The RE and POE were lower in 19/20 (95%) and 14/20 (70%) for the LGA neonates, respectively.

CONCLUSION

There is a wide variation in EFW formulas performance for detecting LGA. Hadlock's formula (1985) combining abdominal circumference, femur length and biparietal diameter ranked highest.