Objective: To explore the reliability of examining the external iliac artery (EIA) at 11+0 to 13+6 weeks of gestation with Doppler ultrasound and its relationship with maternal characteristics and uterine artery blood flow. Study design: Cross-sectional study of 451 pregnant women undergoing an ultrasound scan in the first trimester. Mean pulsatility index (PI) of both EIAs was correlated to maternal characteristics (maternal age, parity, body mass index and mean arterial blood pressure (MAP)) and ultrasound parameters (crown-rump length (CRL) and mean uterine artery PI). Mean EIA-PI was logarithmically transformed to perform multiple linear regression analysis. The intra- and inter-observer reproducibilities of EIA-PI were examined. Results: Satisfactory flow velocity waveforms were obtained from both EIA in all patients. There is a significant negative correlation between mean EIA pulsatility index and maternal blood pressure. Multiple linear regression analysis showed an independent contribution of MAP to log EIA-PI (mean) (standardized regression coefficient = -0.20, 95% CI: -0.005 to -0.002). The intra-class correlation coefficients (ICCs) for intraobserver and interobserver reproducibility were 0.94 (95% CI, 0.88-0.97) and 0.87 (0.76-0.94) respectively. Conclusions: Examining blood flow in the external iliac artery using Doppler ultrasound in the first trimester is feasible and reproducible. There is a negative correlation between mean EIA-PI and maternal blood pressure. © 2012 Elsevier Ireland Ltd. All rights reserved.