[Study of fetal and placental circulation by ultrasound. New technic in the surveillance of pregnancy].

Echotomography has been used for several years in routine for pregnancy follow-up. The morphological parameters provided by this technique (biparietal diameter, transversal abdominal diameter, length of the limbs...) give an objective information on the foetal growth. The exploration of foetal and placental circulation by Doppler measurement has been used in the past for the detection of the foetal cardiac rythm. The association of Doppler and echotomography allows to know precisely the location of vessels of interest, to quantify blood flow volume transcutaneously, and to determine an index of placental resistance. Recent improvements have simplified the use of this complex technique. Transducers for Doppler and imaging have been placed in the same probe very easy to handle. This system allows a precise localization of Doppler sample volume within the vessel to be explored. The great vessels can be studied all long the pregnancy. Normal Doppler spectrum of umbilical arteries shows an important diastolic flow. This fact is related to the low circulatory resistance of the placenta. When the placental circulatory resistances increase (because of placental infarcts for instance) the diastolic flow decreases in the umbilical arteries. To quantify this modification of umbilical circulation we used an index of the resistance (Pourcelot index) [9]: R = (formula; see text) [A systolic amplitude; D diastolic amplitude]. In normal cases, values of R decrease progressively during the course of the pregnancy. In case of abnormal pregnancies (dysgravidy) the index increases. Abnormal values of R had been correlated with hypotrophy or foetus death. With this duplex system it is also possible to determine the different parameters which are necessary to quantify the foetal blood flow in ml/mn. The first results obtained in dysgravidies confirm the major interest of blood flow study in follow-up and prognosis of high risk pregnancies.