Pregnancies complicated by an isolated single umbilical artery (SUA) are thought to be at increased risk for intrauterine growth restriction (IUGR). The management of these pregnancies often includes serial sonographic assessments of fetal growth. The goal of our study was to test the validity of this assertion. We conducted a longitudinal sonographic assessment of intrauterine fetal growth in pregnancies complicated by a SUA. We included pregnancies where fetal growth was assessed three or more times, and the presence of SUA was repeatedly demonstrated. Pregnancies with fetal anomalies and multiple gestations were excluded. IUGR was defined as an estimated fetal weight (EFW) < or = 10th percentile of the normal ranges established by Hadlock. Between January 1999 and December 2005, we identified 273 pregnancies with SUA, for an overall incidence of 0.48% within the total population of patients examined at our institution. One hundred and thirty-five pregnancies did not meet our inclusion criteria. Of the 138 we analyzed, four pregnancies (2.9%) were found to have EFW < or = 10th percentile. We concluded that the occurrence of IUGR in pregnancies complicated by an isolated SUA is not increased. Serial sonographic assessments of fetal growth do not appear to be indicated in the management of such pregnancies.