Difference In Ultrasound Unit Volume Between Birthweight And Ultrasound Derived Definitions Of Fetal Growth Restriction

Recent guidelines recommend the use Hadlock rather than birth weight derived percentiles for diagnosis of fetal growth restriction (FGR). The objective of this study is to quantify the impact of changing from a birth weight (Williams et al.) to an ultrasound based (Hadlock et al.) percentile classification of FGR on ultrasound unit volume. We conducted a retrospective cohort study of all singleton pregnancies that presented for ultrasound ≥22 weeks’ gestation pre- and post an institutional change of FGR classification system from Williams et al. to Hadlock et al. between 2018-2020. Pregnancies with an estimated fetal weight <10% by either classification system were included in the analysis. The primary outcomes were the frequency of patient encounters, follow up examinations, biophysical profiles (BPP) ≥28 weeks, and umbilical artery (UA) Doppler assessments. Secondary outcomes were gestational age (GA) at delivery and rates of cesarean delivery, 5-minute Apgar <7, and fetal death between study years. 550 women met inclusion criteria over the study period. FGR diagnosis was discordant (FGR by Hadlock, but not Williams) in 77.6% of cases at diagnosis and in 46.9% at the last ultrasound before delivery. The median GA at FGR diagnosis was significantly earlier using Hadlock (31.9 vs 36.0 weeks; p