Objective: To determine possible differences in hepatic artery flow between trisomy 21 and euploid fetuses at 11-13 weeks' gestation. Methods: Hepatic artery pulsatility index (PI) and peak systolic velocity (PSV) were measured in fetuses at low risk of aneuploidies (n = 350) and another group at high risk, including 283 euploid and 47 with trisomy 21. The association of hepatic artery PI and PSV with trisomy 21, fetal nuchal translucency (NT) thickness, tricuspid regurgitation, and reversed a-wave in the ductus venosus was investigated. Results: In the low-risk group, the median hepatic artery PSV was 10.0 cm/s and the 95th centile was 14.3 cm/s. The distribution of hepatic artery PI was skewed, but for PI of 2 or more the distribution was Gaussian. In 325 (92.9%) cases, the PI was 2 or more (high PI) and in 25 (7.1%) it was below 2 (low PI). In 33 (70.2%) of the trisomy 21 pregnancies, the PSV was above the 95th centile and the PI was below 2. Multiple regression analysis showed that in the prediction of hepatic artery PSV there were significant contributions from fetal karyotype, tricuspid regurgitation, and reversed a-wave in the ductus venosus, but not delta NT, pregnancy-associated plasma protein-A, or free β-human chorionic gonadotrophin. Conclusion: Trisomy 21 at 11-13 weeks is associated with increased flow in the hepatic artery. Copyright © 2011 John Wiley & Sons, Ltd.