Predictive Value of Fetal Abdominal Circumference in Diagnosing Large for Gestational Age Infants [9D

Abstract

INTRODUCTION: Macrosomia is associated with adverse perinatal outcomes and has implications for mode of delivery. Research increasingly supports the use of fetal abdominal circumference (AC) as an additional measure to capture large for gestational age (LGA) infants. We evaluated the predictive value of sonographic fetal abdominal circumference (AC) measurement from 25-36 weeks' gestation for detection of LGA infants. METHODS: Retrospective chart review following IRB approval. LGA was defined as a newborn birth weight >90th percentile on the Fenton Growth Curve. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) at various gestational age ranges (25-28, 29-32 and 33-36 weeks' gestation) for a Z-score >+1.88, corresponding to the 97th percentile, were calculated. Area under receiver operating characteristic curve (AUROCC) of AC Z-scores ranging from -3.00 to +3.00 was calculated. RESULTS: Ultrasounds of 4801 women with 5799 pregnancies were reviewed. Our study population had an LGA infant prevalence of 5.8%. An AC Z-score of +1.88 had a maximal sensitivity of 34.3%, specificity of 98.2%, and NPV of 96.2% for detecting LGA births at 29-32 weeks' gestation. The AUROCC at this time point was 0.88. CONCLUSION: Fetal AC <97th percentile in the third trimester has a very high specificity and negative predictive value in ruling out LGA newborns. These measures indicate that this modality can identify pregnancies that are not at high risk for fetal macrosomia and would not benefit from unnecessary cesarean delivery. High AUROCC demonstrates independent predictive potential of AC and supports its adjunct use with more traditional measurements.