What does it test for?
Many doctors do an ultrasound (which produces a picture called a sonogram, so the terms are interchangeable) to verify the age of the fetus, see if you're carrying more than one baby, and check for birth defects.
When is it done?
It can be performed at any stage of pregnancy.
How is it performed?
A doctor or ultrasound technician puts a jelly on your abdomen and then presses a wand on it. Sound waves from the wand produce a picture of your uterus on the screen. It doesn't hurt, but the sonogram may be confusing to look at -- your doctor can explain what she sees. The doctor or technician looks your baby over from head to toe, checking, for instance, for signs of a healthy spine and heart. She also checks the placenta, calculates the baby's approximate weight, and examines the baby's position to make sure everything looks healthy.
What if the results are abnormal?
If any problems are suspected, or sometimes just for the sake of extra caution, you may get a more detailed ultrasound exam, called a targeted, comprehensive, or level II exam. It may use more sophisticated ultrasound equipment and will take longer, often more than 30 minutes.