Résumé : A transvaginal colour and pulsed Doppler study was performed on 44 women with normal pregnancies between 5 and 16 weeks of gestation. Maternal levels of human chorionic gonadotrophin (HCG), free α-HCG subunit, free β-HCG subunit, 17β-oestradiol and progesterone were determined in sera obtained at the time of Doppler examination. Uterine peak systolic velocity (PSV) and α-HCG and 17β-oestradiol levels increased significantly (P < 0.001) from the second to the fourth month of gestation, whereas uterine and spiral resistance index (RI) decreased significantly (P < 0.005 and P < 0.001, respectively) with gestational age. Levels of HCG and β-HCG peaked significantly (P < 0.01) during the third month of gestation. Corpus luteum PSV and RI and progesterone levels did not vary significantly with gestational age. Multiple regression analysis showed that gestational age was the only significant (P < 0.05) contributor to uterine PSV and spiral RI variability. In addition to gestational age, 17β-oestradiol had a significant (P < 0.001) influence on uterine RI. Both corpus luteum PSV and RI were significantly (P < 0.01 and P < 0.05, respectively) related to progesterone levels. Corpus luteum PSV was also significantly (P < 0.05) related to 17β-oestradiol levels and RI to HCG levels. These results suggest that: (i) uterine PSV reflects the overall uterine blood supply which increases progressively with growth of the gestational sac; (ii) hormonal factors such as 17β-oestradiol have a predominant role in regulating the uterine vascular resistance changes to blood flow associated with placentation; and (iii) blood flow regulation to the corpus luteum is independent of gestational age and mainly related to hormonal levels.