Don't worry, the baby's heart rate varies from 120 to 160 beats per minute.  Sometimes it goes up to 170-175 when they are very active. When the baby kicks or rolls inside the uterus, then this causes an increase in heart rate.

    The other causes of increase in baby's heart rate is if you are taking  a medication called Brethine ( Terbutaline ) to stop pretem labor or if you're drinking caffeine or any other medication that will also elevate your own  heart rate.  Or if you have fever, then the baby' s heart rate will also go up.