The authors report three years of experience with the use of the Doppler in Obstetrics. Certain notions may be integrated to the principles of clinical decision. The diastolic index D at the umbilical artery increases regularly during a normal pregnancy. It is significantly decreased in case of intra-uterine growth delay (IUGD). When this index reaches zero, it may be considered as a reliable criteria for fetal extraction. Certain notions must be verified: the index seems frequently altered in case of chromosomal abnormality. Some results still depend on research. The index measured at the uterine arteries could predict IUGD and at the level of the fetus' internal carotids, its elevation could be one of the first signs of fetal hypoxia. Finally, the index was measured during normal labor. In case of deceleration it is markedly altered. Thus, this could be an additional element of fetal monitoring.