It's just a monitor they hook you up to so they can see the baby's heartbeat and check for baby movements and contractions. You just sit and relax, it's not a painful test at all. I just had one at my 32 week appt myself so it's mainly exciting cause you get to hear his/her little heart beat.
They can also monitor your bp and heart rate while on the machine. It's a good test to get done.
I get them done twice a week due to possibility of pre term labor and low progesterone levels.
What will they do if I fail the stress test