Objective To review the available literature on outcome of pregnancy when an isolated single umbilical artery (iSUA) is diagnosed at the time of the mid-trimester anomaly scan. Methods We searched MEDLINE (1948-2012), EMBASE (1980-2012) and the Cochrane Library (until 2012) for relevant citations reporting on outcome of pregnancy with iSUA seen on ultrasound. Data were extracted by two reviewers. Where appropriate, we pooled odds ratios (ORs) for the dichotomous outcome measures: small for gestational age (SGA), perinatal mortality and aneuploidy. For birth weight we determined the mean difference with 95% CI. Results We identified three cohort studies and four case-control studies reporting on 928 pregnancies with iSUA. There was significant heterogeneity between cohort and case-control studies. Compared to fetuses with a three-vessel cord, fetuses with an iSUA were more likely to be SGA (OR 1.6 (95% CI, 0.97-2.6); n = 489) or suffer perinatal mortality (OR 2.0 (95% CI, 0.9-4.2); n = 686), although for neither of the outcomes was statistical significance reached. The difference in mean birth weight was 51 g (95% CI, -154.7 to 52.6 g): n = 407), but again this difference was not statistically significant. We found no evidence that fetuses with iSUA have an increased risk for aneuploidy. Conclusion In view of the non-significant association between iSUA and fetal growth and perinatal mortality, and in view of the heterogeneity in studies on aneuploidy, we feel that large-scale, prospective cohort studies are needed to reach definitive conclusions on the appropriate work-up in iSUA pregnancies. At present, targeted growth assessment after diagnosis of iSUA should not be routine practice.