Amniocentesis is done in an examination room, either with or without local anesthesia. It typically takes just a few minutes, during which you must lie very still. A technician locates your fetus with an ultrasound. Using the ultrasound for guidance, your doctor carefully inserts a long, but thin, hollow needle through your abdomen and into the amniotic sac. You should receive Rh immune globulin (RHIG) at the time of amniocentesis if you are an Rh-negative unsensitized patient.