[Behavior of flow waves of the uterine and external iliac arteries during labor contractions].

To evaluate the changes of blood flow velocities of the uterine and external iliac arteries, we studied a total of 15 normal full term pregnant, which were in the active phase of labor. The mean maternal age was 21.6 +/- 5.2 years (X +/- SD), the mean parity was 0.6 +/- 0.5, and the mean gestational age was 39.2 +/- 1.1 weeks. All patients had normal deliveries, the newborn weight was 3440 +/- 621 g, and the apgar score was 8.6 +/- 1.6 and 9.0 +/- 0.7 at 1 and 5 min, respectively. In the uterine artery, the systolic/diastolic ratio and the resistance index increased significantly from 1.83 +/- 0.25 to 4.24 +/- 1.55 (p < 0.05) and from 0.46 +/- 0.05 to 0.74 +/- 0.08 (p < 0.01), respectively from the relaxation phase to the contraction phase. In all 15 patients the external iliac artery showed a reverse diastolic flow during uterine relaxation, whereas only 2 of the 14 patients showed this reverse flow during uterine contraction (p < 0.01). Furthermore, the flow velocity was modified with maternal hyperventilation. Finally, we conclude that uterine contraction induced profound changes in the blood flow velocities in the uterine and external iliac arteries. We proposed that these changes could be explained by uterine muscular contractions causing the blood flow to be shunted to areas of less resistance.