Objective To study the relationship between first-trimester uterine artery (UtA) Doppler velocimetry and birth weight in an unselected, low-risk obstetric population. Methods This is a prospective study of 415 low-risk pregnant women who underwent a first-trimester ultrasound evaluation between 11 and 13?weeks of gestation. Blood flow velocimetry waveforms from both UtAs were obtained and the pulsatility index (PI) measured and recorded. Clinical records were reviewed for pregnancy outcomes. Birth weight was expressed as z-scores, and the Spearman correlation coefficient (?) was used to calculate the relationship between the mean, delta, and lowest UtA PI values and birth weight. Results There was no correlation between the mean and delta UtA PI values and birth weight. However, a significant correlation between the lowest UtA PI value and birth weight (??=?-0.121; p?=?0.013) was noted. Conclusions Our study found a clinically significant correlation between the lowest UtA PI value and birth weight in an unselected, low-risk pregnant population. Because fetal growth is a multifactorial process in which placentation is only one of the factors involved, the use of a single parameter such as Doppler velocimetry remote from the delivery to predict birth weight in a low-risk population seems to be less useful than in the high-risk population. (c) 2012 John Wiley & Sons, Ltd.