Use of a weight indexed umbilical artery systolic diastolic ratio to predict the risk for adverse outcomes among growth restricted fetuses

Background and Objectives: To evaluate weight-indexed umbilical systolic diastolic ratio (UASDR) to discriminate risk for adverse outcomes among growth restricted fetuses (FGR).Design and Setting: Retrospective study using prenatal ultrasound data and neonatal outcome data. Two primary outcomes: admission to intensive care and a composite outcome of severe neonatal morbidity. We included births among individuals with a singleton pregnancy at 24-40 weeks gestation without other indications for preterm delivery. We calculated the percentile of the measured standard UASDR, and the same value indexed to the EFW (iUASDR).Results: 296 pregnancies met inclusion criteria. Forty-seven percent required NICU admission and 31% developed a component of the composite outcome. The sensitivity of the iUASDR increased at lower birthweight percentiles. The positive predictive value of the standard UASDR was higher among fetuses with EFW <5th % and <10th % for NICU admission and composite outcome ((EFW <5th %) 0.82 (95% CI: 0.71, 0.91) and 0.60 (95% CI: 0.48, 0.72) and ((EFW <10th %) 0.81 (95% CI: 0.70, 0.89) and 0.58 (95% CI: 0.45, 0.69) compared with indexed values.Discussion: Data does not support use of the iUASDR to improve the test characteristics of the UASDR. Despite a moderate increase in specificity, the positive predictive value was low. UASDR non-indexed or standard values in conjunction with clinical findings and severity of FGR perform best.