Estimated Fetal Weight and Birth Weight Associated with Isolated Single Umbilical Artery: The University of Utah Experience

Objective The objectives this study were to assess the role of third-trimester ultrasound in detection of fetal growth restriction associated with isolated single umbilical artery (SUA) and to correlate sonographic estimated fetal weight (EFW) with birth weight. Methods A retrospective cohort study was performed from 2000 to 2009 at a single academic center. In fetuses with isolated SUA, EFW at follow-up, birth weight, gestational age (GA) at birth, and pregnancy outcome were compared with expected values derived from a statewide database. Categorical variables were analyzed with Fisher exact test, and t tests were used to compare distributions of birth outcomes to expected outcomes. Results Two hundred twenty-five of 41,821 pregnancies had isolated SUA. One hundred ninety-one had available imaging and clinical data. Of 172 with third-trimester ultrasound, the mean EFW was 51st percentile; 4.7% were less than the 10th percentile for GA. Low birth weight (defined as <2500 g), preterm birth, and stillbirth were significantly more frequent in the cohort than in the state (17.3% vs 5.15%, 19.9% vs 8.0% and 3.5% vs 0.33%, respectively, P < 0.05). Mean birth weight in the cohort was significantly lower (2963 vs 3306 g, P < 0.001) than that in the state. Even in term births, the mean weight was significantly lower than that in the state (3169 vs 3379 g, P < 0.001). Cohort mean GA at birth was 38.1 versus 38.5 weeks in the state (P < 0.05). Conclusions Follow-up growth scans, as performed in this retrospective cohort study, did not reliably predict birth weight. Birth weight was reduced in the cohort even in the subgroup delivered at term.