Sonographic Biometry in the Early Third Trimester: A Comparison of Parameters to Predict Macrosomia at Birth

PurposeTo compare the estimated fetal weight (EFW), abdominal circumference (AC), and femur length (FL), measured on sonographic (US) examinations at 28-34 weeks of gestation to determine the best predictor of macrosomia at birth. MethodsWe retrospectively evaluated 3,857 consecutive, term, singleton pregnancies. The AC, FL, and EFW were compared with birth weights (BW) of >4,000 g and >4,500 g. ResultsThere was a statistically significant association between the AC and FL and a BW>4,000 g or >4,500 g (p<0.001) whether both or either were in the >90th percentile. There was no statistically significant association between an EFW in the >90th percentile and either BW cutoff. An AC in the >90th percentile alone was the best predictor for macrosomia at birth, with sensitivity, specificity, and positive and negative predictive values of 75%, 74%, 24%, and 96%, respectively (95% confidence intervals [CI]: 73-76%, 73-76%, 23-26%, and 96-97%, respectively), for a BW>4,000 g. When an AC in the >90th percentile was used to predict a BW>4,500 g, the sensitivity improved to 88%, but the positive predictive value fell to 5%. Receiver operating characteristic curves comparing the distributions of stratified AC values for BW cutoffs of 4,000 and 4,500 g found the highest areas under the curve of 0.80 (95% CI: 0.77-0.82) and 0.87 (95% CI: 0.83-0.90), respectively. ConclusionsAn AC in the >90th percentile at 28-34 weeks' gestation is the best sonographic predictor of macrosomia at birth. (c) 2014 Wiley Periodicals, Inc. J Clin Ultrasound43:243-248, 2015