Fetal Blood Flow Response to Partial Occlusion by External Compression

Two earlier studies showed measurable fetal hemodynamics changes caused by external pressure induced by te abdominal ultrasound transducer. The investigators would like to study the response of flow in main fetal vessels to different, mild to moderate pressures induced by the abdominal transducer. The pressure induced by the transducer will be measured by a digital computed manometer. The flow chances in fetal vessels will be measured by ultrasound Doppler. Measurements will be taken on different pregnancy weeks, on one occasion in each pregnant woman. Ones without applying transducer pressure (control) and ones after applying mild pressure.