Ultrasound uses sound waves to create pictures of the baby before it is born. Most of the organs and bones of the baby can be seen with ultrasound. This technology is used to identify problems that may have occurred during development with the anatomy of the baby. It is like doing a physical exam of the fetus before it is born. There are no known risks from ultrasound.
While ultrasound is very good at looking at all of the structures of the baby, it cannot always identify problems with how the structures work. For example, ultrasound can see the brain and lungs but cannot tell if the brain or lungs are functioning properly.
Ultrasound exams are done at different times during a pregnancy for different reasons. Early in pregnancy, an ultrasound can establish how far along a pregnancy is or that there has not been a miscarriage. Evaluation of the baby's anatomy is usually done between 18 and 20 weeks after the start of the last menstrual period. Later in pregnancy an ultrasound may be done to follow the baby's growth, the location of the placenta, or to assess the amount of amniotic fluid.
If abnormalities are found on an ultrasound examination, further testing might be suggested. Some ultrasound abnormalities are associated with chromosome abnormalities such as Down syndrome. If this is suspected, amniocentesis may be offered.