After 28 weeks, keep track of your baby's movement. This will help you to notice if your baby is moving less than normal, which could be a sign that your baby is in distress and needs a doctor's care. An easy way to do this is the Count-to-Ten approach. Count your baby's movements in the evening — the time of day when the fetus tends to be most active. Lie down if you have trouble feeling your baby move. Most women count 10 movements within about 20 minutes. Count your baby's movements every day so you know what is normal for you. Call your doctor if you count less than 10 movements within 2 hours.
This answer is based on source information from the National Women's Health Information Center.