1045: Which is better: fetal AC or EFW in predicting SGA infants?

Abstract

Small for gestational age (SGA) is a risk factor for adverse perinatal outcome. Identification of at risk fetuses would allow for interventions to decrease morbidity and mortality of this population. We hypothesize that sonographic fetal abdominal circumference (AC) measurement from 25-36 weeks’ gestation is more effective at predicting SGA infants than estimated fetal weight (EFW). Retrospective database review of singleton pregnancies imaged by one Maternal Fetal Medicine ultrasound unit from 2006-2016. Inclusion criteria were singleton pregnancies with growth ultrasounds between 25-36 weeks’ gestation for whom newborn gender, length, weight, and head circumference were available. Exclusion criteria were multifetal gestations. SGA was defined as a birth weight <10th percentile on the Fenton growth curve. We compared the sensitivity, specificity, PPV, and NPV of AC <10th percentile (Hadlock) and EFW <10th percentile (Brenner) to determine the most effective screening measurement for SGA infants. Ultrasounds of 4801 women with 5799 pregnancies were reviewed. After excluding 119 pregnancies with multifetal gestations, 5680 pregnancies met study criteria. Of these, 459 resulted in SGA infants at birth. The prevalence of SGA in our study population was 8.1%. The sensitivity, specificity, PPV and NPV of AC <10th percentile, EFW <10th percentile, and either AC <10th percentile or EFW <10th percentile are shown in Table 1. At all gestational age ranges, AC had a higher sensitivity than EFW with similar specificity in predicting SGA at birth. As early as 25-28 weeks’ gestation, fetal AC <10th percentile identifies a population at risk for SGA who may have been overlooked when using EFW alone. These pregnancies may benefit from increased surveillance and additional counseling. Although EFW has a very high specificity in predicting SGA, AC proves to be significantly more sensitive. These findings can be individualized to patient populations at varying risk for SGA.