In pregnancies with normal evolution, during the second and third pregnancy trimesters, an increase in the uteroplacental flow is found, which is shown by a decrease in the IR at the level of umbilical arteries. This phenomenon is correlated with a decrease in the wall thickness of arteries from third order stem villi. These changes ensure an efficient materno-fetal gas exchange.


placental morphology, fetoplacental hemodynamics, ultrasonographic examination.