OBJECTIVE: The purpose of this study was to determine whether color Doppler sonogram can accurately depict the placental vascular structures using a latex cast model of the placental vessels, and to make a nomogram of several blood flow parameters according to the vascular structures. METHODS: First, we made 9 latex cast models of placental arteries and performed morphologic observation and measurement. Second, the comparative anatomical observation of placental vessels by color flow mapping was performed for all 9 patients from whom the latex models were made. Third, a total of 102 uncomplicated pregnant women between 18 and 40 weeks gestation were examined by color Doppler imaging. The resistance indices (RI) and peak systolic velocity (PSV) were measured. RESULTS: In the latex cast model of placentas, cotyledons could be differentiated by the presence of independent vascular structure units. First, second, third and fourth branches were noted in one cotyledon. Cotyledons were easily identified and counted by color Doppler imaging. Each cotyledon contained only one first branch of the intraplacental villous artery (IPVA). The number of IPVA-1 on color Doppler imaging was equal to the number of the cotyledon calculated from the latex model. RI exhibited a negative, and PSV a positive correlation with gestational age (p < 0.05 in both cases). At any given gestational age, both RI and PSV in the peripheral arteries were significantly lower (p < 0.01) than those in the upstream arteries. CONCLUSIONS: Color Doppler flow sonography is a valuable tool for detecting the blood flow of intraplacental villous arteries in vivo and the images agree with the vascular anatomy of placenta in vitro. These results may also provide the basic parameters for future studies of some complicated pregnancies.