[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.

[Doppler examination of the umbilical arteries. Its role in the surveillance of pregnancy]. / L'examen Doppler des artères ombilicales. Sa place dans la surveillance de la grossesse.

Pregnancies with a high risk of fetal growth retardation are at present watched by using clinical observations and biological parameters including ultrasound and estimation of the fetal heart rate. The Doppler waveform in the umbilical arteries provides information about circulatory resistance in the placenta. An index of resistance "R" is evaluated on the Doppler trace. The purpose of this study is to describe the score (with its possibilities and limitations) for this parameter "R" to follow-up pregnancies with fetal growth retardation and to compare it with ultrasound, biological and clinical parameters that are commonly used. Two groups of pregnancies have been explored: pregnancies with hypertension and pregnancies with idiopathic fetal growth retardation. Abnormal values of "R" correlate well with failure of fetal growth. Furthermore pathological values of "R" do not correspond to the same population as abnormal values of the other parameters. In some cases "R" is disturbed before the others are. In conclusion, this study shows that the index increases the accuracy of detection and the follow-up of chronic fetal growth retardation, particularly in cases of pregnancies with vascular placental pathology.