[Doppler monitoring of fetal circulation from multiple arteries over several days to improve evaluation of fetal prognosis]. / Monitoring Doppler de la circulation foetale sur plusieurs artères et sur plusieurs jours pour une meilleure prédiction du devenir foetal.

Intrauterine growth retardation and fetal hypoxia are currently related to placental insufficiency. Fetal biometry assessed by echography is entirely adapted to follow the growth and integrity of the principal fetal organs. Hypoxia induces an hemodynamic adaptation which can be detected and quantified by Doppler. The objective of this article is to review the evolution of the fetal Doppler practice for the last 20 years and especially to show that isolated Doppler measurement and only from one site (umbilical or cerebral or aortic) have a moderate negative predictive value of fetal outcome, compared to the study of the fetal hemodynamic evolution (degradation) from several sites and during several days. We will insist on the fact that (a) umbilical Doppler only gives information on placental blood flow and this information does not reflect neither the adaptation to hypoxia nor the consequences of this adaptation, (b) cerebral Doppler accounts for the vascular response to the pO(2) reduction but it does not allow to predict the consequences of this response, (c) the simultaneous study of the placental hemodynamic time course degradation and the cerebral vascular response to hypoxia allows quantification of the cumulative deficit of fetal oxygenation during this period and evaluation the adverse consequences of a sustained flow redistribution toward the brain. Finally, if cerebral vasodilation in response to hypoxia can be considered as a physiological compensatory mechanism, it is associated after several days to the appearance of irreversible fonctional (abnormal fetal heart rate) or organic (cerebral lesions) abnormalities. Adverse effects of this process are illustrated during episodes of acute hypoxia (malaria crisis of several days) or during sustained exposure of the fetus to hypoxia (pregnancy-induced hypertension).

[Effect of cardiac rate on the index of feto-placental circulatory resistance]. / Effet de la fréquence cardiaque sur l'index de résistance circulatoire foeto-placentaire.

Variations of the fetal heart rate in normal or pathological fetuses may induce significant changes of the Doppler indices widely used for the evaluation and the assessment of the placental or cerebral resistances. In case of a low heart rate (120/mn for example), the end diastolic amplitude will be weaker than in case of a heart rate of high frequency (160/mn). This phenomena may explain the great scattering of the normal values of the Doppler indices and the relatively poor sensitivity of this parameter. We tried to minimize the effect of the heart rate on the evaluation of the doppler indices by two methods. Firstly by measuring on the maximum frequency curve the end diastolic frequency for a standard heart rate of 140/mn and the corresponding Doppler index (R'140). Secondly by using a formula giving directly (from the R value on the trace) the value of the index (R"140) for a heart rate of 140/mn. The diagrams of the indices (R'140 R"140) calculated for a standard frequency of 140/mn (on normal and pathological fetuses) show a greater dispersion than the R indices directly measured on the Doppler waveform. Therefore, the sensitivity and the specificity of the Doppler method are reduced. Finally, we conclude that the haemodynamic parameters in the different vascular areas of the fetus can adapt to the heart rate except for very strong abnormalities of the heart rate as it is the case in atrio ventricular blocks for instance. Out of these cases, it seems that the normalization of the index by the heart rate does not improve the accuracy of the doppler indices.