Defining fetal growth restriction: abdominal circumference as an alternative criterion

The purpose of this study is to determine if using abdominal circumference percentile (AC) to define fetal growth restriction (FGR) improves ultrasound at ≥36 weeks as a screening test for small for gestational age (SGA).

All non-anomalous singletons undergoing ultrasound at a single center at ≥36 weeks during 12/2008-5/2014 were included. FGR was defined as (estimated fetal weight) estimated fetal weight (EFW) and/or abdominal circumference (AC) < 10 for gestational age (GA). The primary outcome was SGA (birthweight ≤10th percentile for GA). Data were stratified by maternal race/ethnicity and BMI. Sensitivity, specificity, false-positive rate (FPR), positive- and negative-predictive values (positive-predictive value (PPV), negative-predictive value (NPV)), and areas under the receiver-operating characteristic (ROC) curve (AUC were calculated.

There were 1594 ultrasounds. Median (IQR) ultrasound GA was 37.3 (36.6-38.0), days to delivery 10.6 (5.0-18.4), and delivery GA 39.29 (38.6-39.9). EFW <10 had the following characteristics: sensitivity 50.6%, FPR 2.0%, PPV 83.8%, and AUC 0.743. Using AC <10, these were 64.0, 2.9, 81.3, and 0.806, respectively. Using AC or EFW <10, these were 67.5, 3.3, 80.3, and 0.821, respectively; this criterion has the largest AUC (p < .008). This finding persisted when stratified by maternal race/ethnicity and BMI.

AC <10 is more sensitive and has a similar PPV compared with EFW <10 for SGA. Using AC <10 or EFW <10 has the best balance of sensitivity and specificity as a screening test and has a low FPR. AC may be a reasonable alternative criterion to EFW for FGR diagnosis.