Ultrasonic placental and fetal head localization, although not mandatory, may minimize the risks of amniocentesis for use in genetic counseling. It permits choosing a site other than low midline with a low-lying anterior placenta; with a posterior placenta, the insertion within the amniotic cavity should stop short of the placenta. Although complications of amniocentesis in the second trimester without ultrasound have been very few, it seems worthwhile to try to decrease even this small risk by the use of ultrasound.