Usually to make sure that the baby is where it's supposed to be, as far as position in the womb. They also can check the babies heart rate, sometimes it is hard to tell exactly how well the heart is functioning. If you had other children you know that for whatever the reason the baby tries to get away from the sonogram
A non-stress test is ordered if a doctor senses that the baby is not moving or if there is a placental problem. Usually if the doctor senses there is a risk for any other grounds, this test is ordered. This test does not have any side effects on the baby or mother. For more information about the test, visit http://www.americanpregnancy.org/prenataltesting/non-stresstest.html.