[Ultrasound studies in pregnancy: technical principles and clinical safety].

Ultrasound examinations in pregnancy were carried out worldwide for over 30 years with no proof of adverse effects on either, mother or child. However, to evaluate the clinical significance of the numerous studies dealing with questions of safety of obstetrical sonography, a basic knowledge of its physical and technical aspects is needed. The present paper aims to convey these basics and should provide a review of the major publications concerned with the clinical safety of the method. Below clearly defined intensity levels, ultrasound scanning in pregnancy can still be considered unhazardous for both mother and child. However, it must be borne in mind, that the safety margin of Doppler flow measurements is lower for duplex compared with B-mode equipment. Therefore, for the present, duplex sonography should not be routinely applied in the first trimester of pregnancy.