Determinants of flow along arterio-arterial anastomoses in monochorionic placentae by dynamic computer modelling of chorionic plate vasculature

Examination of the fetal cardiovascular system

Doppler evaluation of the placenta and fetal cardiovascular system is one of the primary surveillance tools in prenatal medicine. By assessing uterine and umbilical arteries, placental development can be documented. This is useful for the prediction of hypertensive maternal disorders and placental dysfunction and fetal growth failure. The umbilical artery flow velocity waveform provides an estimate of villous vascular occlusion in the fetal compartment of the placenta. Middle cerebral artery Doppler is important in studying fetal responses to abnormal oxygenation and fetal anemia. Precordial venous Doppler gives insight into the cardiac effects of many conditions such as fetal growth restriction, twin-twin transfusion syndrome and fetal arrhythmia. Further quantification of these effects requires cardiac Doppler to quantify diastolic and systolic function as well as global myocardial performance. This article reviews important characteristics of arterial and venous Doppler waveform analysis, individual vascular beds and their clinical application in fetal evaluation.

Mise en évidence des anastomoses vasculaires par la vélocimétrie doppler dans les grossesses gémellaires monochoriales. Revue de la littérature à propos de trois cas

Three cases of intermittent absent end-diastolic and reversed end-diastolic flow velocity (A/REDV) are reported in the proximal umbilical artery of the growth-retarded twin in monochorionic twin pregnancies. This typical doppler velocimetric pattern has been related to arterio-arterial anastomoses in two cases of intra-uterine growth retardation and in one case of twin-twin transfusion syndrome. According to the literature, superficial arterio-arterial anastomoses may be detected by doppler colour velocimetry in 75 to 85% of cases, while identification of arteriovenous connections is more difficult to be documented in vivo (50% of cases in experienced hands). The role of superficial vascular anastomoses, either arterio-arterial or venovenous, and that of deep arteriovenous communications is now well documented in the main complications of monochorionic pregnancies, particularly for twin-twin transfusion syndrome, intrauterine growth retardation, intrauterine fetal death and acardiac twins.

Replacing animal experiments: choices, chances and challenges

Replacing animal procedures with methods such as cells and tissues in vitro, volunteer studies, physicochemical techniques and computer modelling, is driven by legislative, scientific and moral imperatives. Non-animal approaches are now considered as advanced methods that can overcome many of the limitations of animal experiments. In testing medicines and chemicals, in vitro assays have spared hundreds of thousands of animals. In contrast, academic animal use continues to rise and the concept of replacement seems less well accepted in university research. Even so, some animal procedures have been replaced in neurological, reproductive and dentistry research and progress is being made in fields such as respiratory illnesses, pain and sepsis. Systematic reviews of the transferability of animal data to the clinical setting may encourage a fresh look for novel non-animal methods and, as mainstream funding becomes available, more advances in replacement are expected.