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

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.

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)].

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.

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.