It's a none stress test , I went through a few days where I didn't feel my baby move so I was sent to have the test done to monitor his movements. they hook you up to a monitor and record the heartbeat and movements for about 30 minutes
once a day is fine, since your baby will have sleep cycles, my OB didn't say anything either but when I went to have my nst test done the nurse told me to do it and that it's important to do.