OBJECTIVE To investigate the maternal serum concentration of insulin-like growth factor-I (IGF-I) in the first trimester of pregnancies that subsequently develop preeclampsia (PE) and to examine the possible association with uterine artery pulsatility index (PI). METHODS The maternal serum concentration of IGF-I and uterine artery PI at 11-13 weeks were measured in 53 cases that developed PE, including 18 that required delivery before 34 weeks (early-PE) and 106 unaffected controls. The measured IGF-I concentration and uterine artery PI were converted into a multiple of the expected median (MoM) in unaffected pregnancies, and median MoM values were compared in the outcome groups. The significance of association of IGF-I MoM with uterine artery PI MoM was determined by regression analysis. RESULTS In the early-PE and late-PE groups, compared to the unaffected controls, the median IGF-I decreased (0.53 and 0.55 MoM, respectively) and uterine artery PI increased (1.55 and 1.21 MoM, respectively). In the group that developed PE, there was no significant association between serum IGF-I and uterine artery PI (p = 0.632). CONCLUSIONS In pregnancies destined to develop PE, the circulating levels of IGF-I decrease from the first trimester of pregnancy suggesting that IGF-I may be implicated in the pathogenesis of the disease.