(533) Comparison of fetal abdominal circumference references for the prediction of SGA

Small for gestational age (SGA) infants are at increased risk for adverse neonatal outcomes. Fetal growth restriction (FGR) is defined as estimated fetal weight (EFW) < 10% or abdominal circumference (AC) < 10%.  In the United States, the Hadlock reference is the most widely used method for estimating the fetal AC, however, several other methods exist including the INTERGROWTH-21st standard and the Chitty standard. We sought to compare the ability of three antenatal AC standards to predict SGA and adverse neonatal outcomes.

Study Design: In this secondary analysis of a cohort of singleton gestations that underwent fetal growth assessment between 26 and 36 weeks of gestation, fetuses with chromosomal or congenital malformations and those without delivery information were excluded. The Hadlock, Chitty, and INTERGROWTH-21st fetal AC methods’ ability to detect SGA and adverse neonatal outcomes were compared by calculating the area under the receiver operating curve of clinical characteristics, sensitivity, specificity, positive predictive value, and negative predictive value.

Results:

Of 1054 patients, 122 had an AC < 10% by Hadlock, 31 by Chitty, and 50 by INTERGROWTH-21^st (Table 1). The Hadlock definition for AC < 10th was a better identifier for SGA. AUC and 95% CI for SGA for Hadlock, Chitty, and INTERGROWTH-21^st were 0.73 [0.69 -0.77] vs 0.59 [0.55 -0.61] vs 0.62 [0.59-0.66]) (p< 0.001), respectively (Figure 1). All AC standards had suboptimal performance for the prediction of adverse neonatal outcomes.

Conclusion:

The Hadlock AC < 10% was a better predictor than Chitty or INTERGROWTH-21st for SGA. All references had a suboptimal ability to predict composite adverse neonatal outcomes. The Hadlock reference chart should be utilize in obstetrical practice.