A test in which pictures of the developing fetus are made from sound waves. This painless and safe procedure is used in hospitals and many doctors’ offices to determine the age and rate of growth of the fetus and its position in the uterus. Ultrasound can also be used to identify multiple pregnancies or a visible birth defect, and it is used to show the position of the placenta and amount of amniotic fluid. Certain procedures, such as amniocentesis, chorionic villus sampling, and fetal blood sampling, are guided by ultrasound. Most pregnant women in the United States will have at least one ultrasound examination during a pregnancy.