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The aim of this study was to describe changes in umbilical artery blood flow in the later stages of canine pregnancy. Seventeen pregnant bitches were examined sonographically to evaluate umbilical artery blood flow at the following antepartum times: 120–96, 96–72, 72–48, 48–24, 24–12, 12–6 and 6–1 h. The peak systolic velocity and end diastolic velocity were measured to calculate the resistive index (RI). Bitches were classified into two groups according to delivery method: normal delivery (Group 1, n = 11) and Cesarean section, due to fetal distress, (Group 2, n = 6). During the study, the RI of the umbilical artery in bitches in Group 1 significantly declined in the time periods 72–48, 24–12, 12–6 and 6–1 h before delivery when compared to the reference RI (120–96 h antepartum period), with values ​​below 0.7 in the 12–6 and 6–1 h periods. In Group 2, the RI decreased significantly in the antepartum periods 96–72, 72–48, 48–24 h with respect to the period 120–96 h, and increased in the periods from 24–12, 12–6 and 6–1 h (being significantly higher in this last period) until the time of Cesarean section. Therefore monitoring of changes in umbilical artery RI in the pre-partum period may provide information about time of delivery in bitches and also assist in the diagnosis of possible dystocia and fetal distress.